Nice project, but now you've discovered on your own another of the reasons not to try to use the ONE-PART putty for heavy fills. Even though it's "Bondo brand", it's NOT BONDO. The generic term "bondo" means a TWO-PART, catalyzed polyester putty. The red stuff you're using is a one-part LACQUER PUTTY. Lacquer putty contains lacquer thinner, which is a solvent that melts plastic. When the one-part putty surface dries, the lacquer thinner goes down into the plastic instead of evaporating off of the surface. Result...sometimes badly warped model parts, as you've now learned.
Another one of those warning signs about the folly of over-reliance on technology. Sure, it's great when it works. And when it doesn't, if there's no backup plan in place, everything stops. But hey...most everyone seems to live in a la-la-land where computers never crash, all data is secure, the power never fails, ad nauseam. Many systems this society increasingly depends on are horribly vulnerable to a lot of things besides weather. Might be time to take a little time-out for a reality check.
What Mark said. A decent (not 5-minute garbage) epoxy-and-microballoon slurry is probably your best bet to stabilize the groove (rough it up IN the groove thoroughly first to guarantee adhesion), then repeated primer / block sand / primer / block sand on top until you can't see any ghosting in the primer.
Thanks to everyone who's followed and expressed interest. Rob, the hood, hood sides, nose, front and rear bellypan sections and hard tonneau will all be copied in molds made from the original parts shown here, and the final model will be assembled with those components being openable and / or removable. The parts, as shown here, are all klugey cobbled-up looking things on the hidden sides, just plugs for the molds to be made after the thing is painted. I've shown my technique of making almost-scale-thickness real fiberglass parts on several WIP threads on this and other forums over the years. I've been honing the process, and can produce a near-perfect copy now. From another of my track-nose builds...plug on the left, mold in the center, copied part on the right. http://www.modelcarsmag.com/forums/topic/66744-chopped-34-track-nose-3-w-coupe-new-nose-finally-july-13/
More recent type of mold on the left, copied part in the center...
The completed parts are very thin, and because of the exceptionally high-strength of the 1:1 aviation materials I use, they are significantly stronger than either resin or styrene, and don't warp over time.
Less than 60,000 original miles, mostly original paint, original mouse-fuzz interior and faux woodgraining. Just got a new clutch, brakes, tires and a heater. Rewired several years ago after rats got to the fabric insulation on the old harness. Runs smooth, starts instantly.
Richard's right...definitely 1/32. When I first got back in the hobby in '05 or so, I got all excited seeing some of the smaller scale kits of '50s iron, and assuming they were 1/25. There IS an old Revell 1/25 '57 Caddy...
Here are some concept workups that look good to me...much better than the ungainly turd in the opening posts. The yellow and red ones may be a little too Camaro-ish, but not bad overall. Apparently the plan is to market this thing world-wide, so taking a lot of unnecessary pork out of the current Challenger was the reason for going with an Alfa Romeo-derived platform.