Aircraft are compromises and neither wood, metal, nor plastics will present a perfect solution to the design problem. If you want to be safe and don't want to strain your brain, just build per plan. If you want to get a little more performance out of your project just do the research and make reasonable changes. Also, be sure and check out your work by doing tests. For example, if you want to significantly improve the chemical resistance of your composite fuel tanks, line them with DOW Derakane resin.
Auto gas is no problem.
I tested it. If your airplane is a first, second, or third generation composite, paint it white and try to store it in a hangar. If you want a high quality part which will far exceed the performance of aluminum use high temperature toughened resins, AS4 carbon fiber or better, and compatible core materials. After all, your uncle does. Composite surface impacts will cause damage to the structure, but in most cases the structure is redundant enough to allow for it.