Fiberglass is a "living" thing. It "never" stops moving. The dark color thing is based on "absorbing" more heat, which promotes swelling, and of course shrinking when it cools again. I'm not sure that the color makes that much difference in the direct sun, which is in the summer when we use these cars the most. The frustrating thing to some folks is, they will spend a gang of time blocking, priming, blocking, priming, working to get the car surface "flat". Then they paint it. At the next rod run, they're parked in the sun, sittin' in their easy chair, and look over at the side of the car. What do ya know, the friendly car has more waves than a New Years day float full of parade queens. Dark colors will show that more. That evening, the worried rodder has his baby safely tucked away in the garage. He goes out to take another look under the flourescent lights, and the sides look "flat" again. The car's cooled down and the body has moved back again.

Prep at the beginning will help with reducing the severity of those instances. Bolt the new body (the "fresher" it is the more important it is) to your chassis, sand every square inch with 80 grit paper on a block (straight strokes, not circles) to open up the surface of the gel coat, and then put heat to it. If you have a heated booth, roll it in there and crank it up to 150 or so. Otherwise, roll it out into the sun. You'll smell the off gassing. When that diminishes to nearly nothing then you cure is better. Some of the companies claim that they will run their bodies through a bake booth to do that for you. The others that don't have the facility to do that will probably deny the need for it.

Chopper bodies have many detractors, but properly done they can be quite durable. Look at all the boats out there that take a pounding on the water and survive well. The usual benefit stated for hand laid, besides the strength issue, is consistency of thickness. Of course the chopper guys will claim that if it's done right, the sprayed body will be consistent too. And a sloppy hand layer can leave voids, folds, and other quality deficiencies as well. And there is where it ends up. A quality shop will do a quality job, a hack will hack it out. Despite the process used. I do like the shops that use "Core mat" for reinforcement of large "flat" areas, such as floor, door skins, and roofs. On my Gibbon, they didn't do the trans hump at the factory, they ship it loose, presumably for access. When I glassed mine in, I reinforced it with core mat, made the floor very rigid.