My question is, can I use fiberglass instead of metal?? It should accomplish basically the same effect, although I have been told fiberglass won't stick to metal for any length of time. And the holes from my spoiler are poking up from the trunk, sort, hard to explain. I could probably just dremel them down, right?
If I mess up the first time I have all winter to get it right since I found a winter beater. Seven months to do bodywork so I've got all the time in the world to learn...

don't grind them down...I know what you are talking about.If you don't have a way to weld them closed gently tap the holes so they creat a divot for filler.I know there isn't really a way to put a backer under the hole while you make then flush so just gently tap them down.then use you dremel to prep the surface so the filler WILL hold.If done right it will last a very long long time.Try to epoxy small pieces of tin under the hole.Before you do use a center punch to make divots in it to help hold the filler then epoxy them under the holes.I'm sure every one has there own way to do it this one has worked for me with some other cars and is still holding strong.I brazed mine closed on my car but if you don't have the tools to do that this is another good method.Cheap,fast and effective.

I heard to use the pointy end of a bodyworking hammer to hit the hole inwards so that it is inside out then how it is now (ie. pointing to the inside instead of the outside) and then use body filler, and so on, and then I also read Pushin420A's way of using something to hold pieces of metal on underneath use something like JB Weld and then only using bondo for the actual hole itself, but really that seems like a different way of doing the exact same thing and in the end I would still have to knock the hole down and use a bunch of filler anyway.

I know the muscle car guys do it by bending metal and cutting everything to fit, welding it in, and then sanding all of that down (using hardly any bondo) but I'd rather not mess around with a project like that, our trunk curves in more then one direction too which makes it complicated.

Originally posted by BumpinTalon
but really that seems like a different way of doing the exact same thing

Yea it is the exact same thing really and both ways work great.epoxy jb weld it's kinda all the same....once the bondo grabs it really doesn't matter.