"TJ Mac"....Typically the gelcoat gets dry and oxidized and then when you apply polish, the pad wants to skid on the dry parts and leaves you with that uneven look. All of the suggestions above are really the way to get the shine back, but require some work.
I had a Class C for fourteen years that I waxed at least twice a year. It had a corrugated fiberglass finish which was brutal to wax. Eventually, after about ten years, the one side and corner that got hit by the California sun, just dried out. Waxing was a pain. This was about 15 years ago so the Zep floor wax had never been tried and there weren't as many products or people talking about them.
Here is what I found that worked and seemed to last between wax jobs. As I waxed, I used a can of Pledge spray wax. I would spray the area where I was going to wax with the Pledge and then wax that area. It put moisture back into surface and made it easier to apply the wax without it skidding or leaving an uneven shine.