Its not that youre wrong…Im just using my experience with Bondo…if you build it up thick youll find that it will end up shrinking and cracking out.
At the very minimum Id thin it with some resin and pack it full of chopped up matt or strand to give it something to pretend it wasnt going to shrink.
And if you use the bondo…do it slowly with thin coats letting them shrink for about a week at a crack. Then if you have problems it wont be deep ones.
There is Bondo already made like this with chopped up fiberglass mixed in… the mix is green in color and so is the can it’s sold in. It’s not thinned with resin though so you would have to thin it with resin yourself. It’s harder to sand than normal bondo… not impossible, just takes more time is all. Marglass also makes the stuff and guess what… it’s green in color and has fiberglass mixed in it lol.
My guess is the green bondo will expand and contract more closely to the SMC or fiberglass panels than steel/bondo. How deep is the valley your wanting to fill in?
edit: ohhh duh you guys already said this lol. On the subject of regular bondo… i’ve used it a lot and mine has never cracked out. I’ve slammed the doors it’s on, flexed the panels and it never seperated from the steel panel or cracked. Granted i didn’t do a massive flex test. Usually if it cracks or seperates (falls off) it’s from the prep work not being good enough. On metal ya gotta rough the crap out of it with 40-80 grit paper before applying the bondo filler. And mixing it at the correct ratio. 
Im pretty sure most fabricators will tell you the same thing I am…
On shaved door handles…the bondo always ends up cracking out. The door skins are too thin and flex too much.
As far as the vette…I wouldnt risk it and just use the epoxy. Id hate to see a nice car end up messed up 2 years down the road.
Bondo is for doing spot work.
I can see around a shaved door handle on some cars and trucks… Nissan made some pretty thin sheetmetal panels on their 80’s-90’s trucks.
Ok. I now have the entire beltline removed and the car looks better already! No more cheesey 80’s beltline clashing against the paintjob! The only problem is I am thouroughly confused about which product to use to fill the gap. I tried to take pics, but my digital camera took a dump. I will go to Wal-Mart and get a cheap one so I can upload pics for you guys. The beltline is the first of several mods I am doing to this car. All are subtle modifications that correct in my opinion the “design flaws” to the car which will make it a beautiful car (more than it already is). I like to clean things up rather than the ridiculous rice mods I see on the streets out here in SoCal. Something tells me this site will be handy. I am going to wait on asking questions about other mods until I figure out the belt mod. Thanks for all your help so far. I will be doing a pic post soon which will show you exactly where I’m at and what I’m going for. Thanks again everybody!
Confused about ??? We gave you the best options in the previous posts ?I don’t understand where the confusion would come from really.
Just go to the auto supply house locally that carries bodyshop supplies and ask for Dyna-hair and buy the good green wide 3M tapes whilst there. And get to back filling. Of course AFTER you’ve sanded and prepped the valley.It wouldn’t be a bad idea to drill some 1/4" holes in the valley to aid as anchor holds too.
Vinny
If you need to surface steel body panels, and you only need a thin skim to get level, then its best to forget about body fillers (which can crack and fall out if applied very thinly), and use lead. This is the method that was used in the past, and is still used in quality restoration jobs of valubable classic cars.
Corvettes have always been fiberglass bodied from the factory.
Might be a bit difficult using lead then…lol
I guess I am confused because I have bondo fiberglass reinforced filler in my garage I bought for this but a few people on this site and guys I know say it’s crap and it will shrink and have issues. I’ve been told use Rage, Bondo, MarGlass, and Dynahair. I guess I will get the Dynahair. What’s the tape for? And if you think I am being hesitant to just throw anything on the gap then you’re right! I would rather be ridiculously slow and consider ALL opinions than to just throw a bunch of cracked garbage that ruins my vette. Sorry. I am a perfectionist. Thanks again!
If your up for expiramenting with bondo you can ad gelcoat to it and catylize it with MEK instead of the cream hardner. Supposed to be pretty durable.
I prefer 3M’s vinyl ester filler myself.
Body filler made with aluminium, rather than talc is probably going to work a whole lot better in any application where there are shrinkage issues.
Being cautious in unfamiliar subjects is always good. I didn’t mean to come across harsh there…if I did?
Anyway…the Dynahair is Polester short strand glass and resin.
I’m wondering if the Vettes is made of FRP in your era ? It may require something more like a DynaWeld by Dynatron ? Its a Epoxy adhesive filler product that might work best. Its about 20$ per dual tube kit.
The wide green tape is to hold/dam back the filler til it kicks/cures.
Vinny
Im sticking with the durabond or two part epoxy via quart cups.
SO am I.lol.
Vinny