For many years now, I have been using a product line from Liquid Tech called First Finish.
I discovered the product at a swap meet display years ago.
It's not cheap, but the finish is mind-blowing.
Saw the same fella a few years later at another car show and asked him if they made a specific cleaner and wax for fiberglass boats.
He gave me a free sample, and I tried it on my Dad's red fiberglass boat, which had sat outside for about 40 years, and the red was a chalky pink.
It took a while to polish it by hand, probably more than 40 hours total, but by the time I was done, it looked like a new boat.
The car stuff is a two-stage system.
After a good wash and dry, you use the prep/cleaner, apply and let dry just like wax.
After polishing off the cleaner, apply the "wax" (it's actually a polymer).
The "wax" has to dry for at least 15-30 minutes before you w buff it off.
It can be applied in direct sunlight (it actually works better there).
You can even leave the "wax" on the paint for months, and it will simply buff right off, unlike natural car wax.
The company even recommends applying it when you park the car for the winter, and it will buff right off in the spring with a soft micro-fiber cloth.
And it will, I've done it.
As I said, mind-blowing. It will even work on the decals.