Ahh, the curse of the gel coat! Before I got my Winnebago Adventurer 38R with full body paint, I owned a Monaco La Palma that had been in the sun for years and its gel coat was very dull. I stripped the decals off and had the graphics repainted on in their place. I also had them buff all the gel coat. They didn't do a very good job either, so I decided to do it over again myself. I am experienced in paint and body work so I first used my 9" buffer with a wool pad and various rubbing compounds with a little improvement. Using that combination worked but it was a mess and hard to be consistent. I then went to Harbor Freight and bought this orbital buffer with the orange coarse pads. You'll spend less than a $100 and mines buffed the La Palma three times plus waxed my Winnebago a couple of times, plus automotive work. I just bought another one for a backup if I ever burn this one up. So far its been bulletproof.
There are grey and blue pads are for polishing and waxing too.
Then I finally found a compound that really worked, Presta Gel Coat Compound. It;s not cheap, about $40 for 32 ounces.
You might find it locally at an auto body paint and supply store or online at Amazon, Ebay or many other places.
I suspect your professionals used a cleaner/wax with no results. The problem is your gel coat needs to have the top dead layer of it buffed off and smoothed. It can then be waxed to protect it. It is a tedious time consuming process and if your coach is exposed to the sun 24/7/365, it will need to done yearly. Do a small area at a time, (3' X 3') until it shines deeply. You'll notice your pad will turn white and be caked with compound and the dead gel coat. You can switch to a new pad while that one dries, then blow it out with forced air and use it again. It will take several days or more and you'll probably use up a pad and half the compound each time you do it. Like anything, the more time you spend doing it and the more experience you get, will make it worth it in the end.