Again, if you can afford it, Styroplast will give you everything you are asking for:
- Strength
- Ultra Lightness
- Just the right amount of flexibility so it won't crack but also won't dent easily
- Not only water resistant, but resistant to most chemicals including gas
- Won't crack in the sun even if not painted
- Can be made very smooth even when brushed on (it is somewhat sandable too)
- Can go on thick or thin and can be coated over itself (note that it has to be primered unless you paint it within a few hours after it sets up)
- Bonds to most surfaces even if they are not porous.
- You don't need to use mesh with it, but you can if you want it to be incredibly durable
- The toxic component in Styroplast is the same toxic component in super glue
- After it dries (after approximately 2 hours) there are no VOCs
It is fairly costly, but it is the final encapsulant - much less expensive than a paint job on a car, but it is the actual shell and finish.
Foam Coat with Bounce is much more rubbery and a bit heavier than Styroplast. You actually start with the Bounce, which is $70 per gallon, and add Foam Coat until you get the consistency you desire. It will probably be 80% Bounce. If you add water in place of Bounce, the coating will lose much of its rubberiness, but will still be quite crack and chip resistant - and save $ if that is important. It's difficult to describe the qualities. The white, beaded EPS foam has a memory, so if you press on it, it will spring back to an extent. That being said, if you press it hard enough, the foam will cave in under the coating and the dent will be permanent. This stuff cannot be sanded, so it is difficult to get a perfectly smooth finish.
I believe Foam Coat by itself will be too heavy and brittle for your foamies.