Dull finish on motor home of friend

I kind of wondering if the fact I have full body paint (More resistant to sunlight) and wax 2x a year makes any difference (most of the RV looks as good as the day I got it... Some nicks and scratches, but most of it is pristine.)

Keep in mind that unpainted fiberglass RVs are attacked by the sun just like the newer plastic lens headlight assemblies. Looking with a microscope, you will see the surface is no longer glass smooth. Power polishing the surface can bring the shine back just like polishing kits get those headlights looking good again but in both cases, the dullness returns quickly. Also difficult to power polish without inadvertently hitting any striping and damaging it. One of the components in fiberglass (and headlights) is UV protection and as the years pass, ultraviolet from the sun destroys it so that whatever you do, the shinyness cannot be kept very long. When an RV gets really dull, the only lasting fix is to just have it painted. The paint will stop further sun damage to the fiberglass in it's tracks and if normal automotive grade paint is used will last 10 years.

I've heard about Zep also, but from experience with a kitchen floor, I know it yellows with age and heat. Our motorhome has a lot of white on it, so don't want it yellowing and have to try to strip all that wax. We need to do our front and rear caps, which are fiberglass and starting to oxidize. Planning on going to a boat place to buy something specifically made for fiberglass.

Are the sides fiberglass?

Zep is an interior floor finish and will do nothing to protect the surface. It will oxodize.
If the outside is fiberglas, then there are lots of products designed for it. 3M, McGuires both make excellent products designed for fiberglas boats and RVs. It will take effort to make it look good again, and it takes effort to keep it looking good.