Ok, quite a few of you have been asking, so I'll attempt to do a scribble on fitting these panels...
Grinder with cutting & grinding discs, wire brush bit & sanding flap disc.
Electric drill & bits
Safety goggles, ear muffs, welding helmet etc
13mm socket & spanner
17 or 19mm socket & spanner
Cross head screwdriver
Felt tip pen & ruler
Lots of G clamps & molegrips
Complete rear quarter panel
Spare sheet (for surrounding areas)
Time taken: A weekend to a week - take your time, measure thrice, cut once (1st one took me a week of evenings, 2nd one a day)
Before doing any welding always disconnect the battery.
Take off the rear wings, running board and bumper. If your car has a Z bar that bolts to the inner rear wings, remove this too. Pop out the side rear window on the relevant side and undo the rear body bolt (either 17 or 19mm) holding the body to the chassis in the inner rear wing. Also, if it's still in, remove the lower section of the headliner that runs under the window and down the B post behind the seatbelt. Finally, remove the door strike plate and seatbelt from the B post, but leave the door in place. If you are going for a full resto it is also worth digging out some of the foam between the cabin and engine bay and pulling the loom through and out of the way if you are going the passenger / n/s side.
The panel also needs some prep. cut off the top of the window frame, leaving plenty of overlap where you want to cut the B and C posts. Clean up the edges along the bottom where it meets the channel, inside where it meets the arch, window opening and a post seam. Drill a series of holes down the a post seam and the window aperture. You can spot weld the rest but I usually seam the other places to stop moisture getting in, choice is yours though.
The first cut
Before you attack it with a grinder, you need to decide where to join the new panel to the original. The new quarter goes right to the top, under the roof of the bug. This area is a real pain (lots of panels joined together) so I wouldn't advise going anywhere near it. I usually cut the panel in through the A post (see below) and across the c post so that it meets where the end of the roof panel joins the quarter (pic 3 below - open the engine lid, look up towards the top, where the roof seam ends and you'll see a join there). This way avoids problems with curves and gives you a nice flat join to skim with filler post-welding.
*If you are replacing the side the loom goes through be VERY careful cutting as the last thing you want to do is slice the loom.* I usually cut a little bit off, pull out the foam insulation which gives enough room to wedge the loom up out of the way. Or, remove it completely if you like.
Now, fire up the grinder and get cutting!
B post - cut this 2/3 of the way up the window opening. We'll trim this back later.
C post - straight across here but cut it a few cm below where you want to eventually join the panel - it's a lot easier to remove excess metal than replace when you've cut too much off. also try and avoid going into the roof seam at the back. If you curve it under the last cm or so, it gives a factory finish without the aggro (see pic 3 & 4 above).
Heater channel - the panel is joined to the side of the heater channel behind the running board. Either undo the spotwelds or chop it off with the grinder
B post - see those 'claws' that hold the rubber edging of the headliner in? (pic 4 in preparation) - look to the side of then and you'll see a row of spotwelds going down the B post. Remove these.
Rear valance - you can unpick this too but it's often easier to cut it off and replace with a new one
Engine tray - there's a new engine tray on the panel, so carefully cut out the old one where it joins the engine firewall horizontally.
Inner rear wing - look to the left of the main chassis bolt (towards the back of the car) and you should see a row of spotwelds. These hold the panel to the side of the firewall.
Boot floor / corners - often an area that's been repaired before, so remove this along the join between the 'boot' floor (behind the rear seat) and the inner corners under the seat. It's easier to see this than explain it so pic 4 below should give you some idea (grey is the new panel, red the bug).
Remove the above by either drilling out the spotwelds or by careful use of the grinder (cut through 1 layer of metal and then peel it off). when it's all off, you should be left with something resembling pic 1 above.
Trimming the panel to fit
This is the time-consuming bit as you need to offer up the panel, trim, refit & repeat numerous times
Now offer up the new panel and mark where the cuts in the B and C posts are on it. Take the panel off and add a couple of inches to these marks so that you take off less metal and you still have an overlap. Check again against the car and then cut the top of the rear quarter on the panel off.
You should now be able to more or less put the panel in place with minimal overlap. You should be able to stretch the B post a little so the new panel will wrap around the old one.
Clamp the panel around the window opening, making sure it fits flush & no higher than the inner window panel (you don't want to have it all done & find you can't fit the windows). These panels are usually spot on in terms of measurements but you could always make a card template of the window whilst stripping the car if you like. At this point I usually trial fit the door to make sure the gap stays even all the way down. Don't forget about the body-chassis bolt in the inner rear wing (pic 8 above) and the little rubber spacer that sits underneath it
Now mark the panel on the b post. Mark on a horizontal line all the way round the panel and cut through both the new post and old post with the hacksaw at the same time. This should give you a perfect fit & the right gap (the width of the saw blade) for welding once you remove the off-cuts - see pic 1& 2 above. Clamp this in place.
C post - trickier & much more time-consuming, but trim a bit off, offer up, see where it's at in relation to the line & trim a bit more until you are close enough to the lign. You have a choice here to either joggle the panel using a joggler (it puts a step in the panel so the bottom one slides under the top one - pic 9) or butt weld it. If you are butt welding it you will need to keep trimming and fitting until you are spot on.
Joggling is quicker but you will need to get waxoyl in behind the panel once done to stop any condensation pooling in the joggle.
Once you're happy with that, clean up and areas that need it for welding and trial fit the door, running board, rear wing & rear valance if possible just to make sure everything is ligned up 100% before any welding takes place. I usually take this opportunity to paint the inside of the box sections too (but then I probably need to get out more!)
Let the welding begin
Now the bit where you feel you're actually getting somewhere! Use a damp rag to take the heat out of the panel and weld in short bursts to avoid as much distortion as possible. Check everything ligns up again (door gap etc) and clamp it in place. Tack the new panel to the bug in a few places and then fit the door striker plate to the B pillar and check to door opens and locks ok. Once happy, weld the rest in. I usually weld a bit in the middle, then the back, then bottom, then b post. this way heat doesn't build up too much in one place and the panel doesn't end up being stretched or pulled to one side. The last bit I usually do is the boot floor bit (pic 6 above). Once it's all in place, remove the clamps and clean back the welds. Due to the gaps left by the saw blade on the posts, you should be able to grind the welds flush. Best thing I've found for this is a sanding flap disc that goes on a grinder. It's made up of lots of little bits of sandpaper. Grind down the rest of your welds so they look nice & tidy.
Finishing it off
Filling - baremetal the area to be filled first - filler must go on bare metal or it'll fall off.
B post - only a very light skim should be needed here where you cut through the window opening. Where you welded the back of the post (where the seatbelts go) will be covered by the headlining so no need to fill here.
C post - slightly more filler probably needed here than on the b post. Using a sanding block, level it and sand down, then repeat until it's all nice and smooth. you will probably have to put another thin skim on to get the finish spot on. I usually use 180 or 240 grit to (very) roughly shape the filler, then 350 for finer and finish with 800 and a final once over with 1500. Finally, cover the area with some etch prime prior to primer.
A bit long-winded but this way means you have no sanding marks to deal with. It should now look like pic 1 below and when painted should look invisible (pics 2&3)
Bit of paint, put everything back together and go brew a cuppa
If you don't need the full panel...
Of course you might not need the full panel every time. In the pics below I had a big dent in the rear quarter and only the front part of the wing mounting panel was rotten. I'd managed to get a 2/h panel for £20 so used a section of that following similar methods to above.
For more pics also see: 1302 Project bodywork parts 1 and 3