How hard is it to replace the fuel cap side quarter panel? (just the skin) is this a massive job? will the chassi loose some of its strength after a new piece is aplied,
is it expensive. I have a lot of dents and have just found filler all the way down the b pillar.

 

I had a shop quote me $900USD a side on a 323GTX that I have, That included the panel which I found out was $485-500USD ea. new. I went to a salvage yard bought the pieces for $75 a side and did it myself. It was a nice feeling saving almost $1650, it was a pain to do but worth it. If done right the chassis will be fine. If you can't do it all yourself, get a quarter panel from a salvage yard, get it ready to install by cutting it close to fit. Split seams where the car is put together as much as you can(door jamb area, under the hatch seal etc.) then let someone else finish it. You'll save a lot of $$$ that way.