Gelcoat is like fiberglass resin. It is heavy. Over the entire outside of a unit gelcoat, coloured or not, adds a lot of weight. Builders are always looking to minimise weight so specs on gelcoat thickness will be minimal.
You can see the difference between RVs & boats. Weight is not so much of an issue in boats & foot for foot boats cost far more than RVs.
Basically, if you buy new, keep it looking like new with regular maintenance of wax or protectants. Once the surface is faded & chalked you are now removing already thin material to get a shine back.