Years ago, I owned a manufacturing concern that used fiberglass reinforced panels for specific projects, so I have some experience with the material.
More directly, you used a product that is an abrasive, ie: practically identical to a 'fine cut' paint compound. It removed the gel from the FRP. I haven't mic'd the frp on my trailer, but I know from experience the usual thickness of the panel is between 3mm and 5mm. I'd be willing to bet it's 3. Because the fiber threads are visible in undamaged panels, the gel itself is most likely not even 10% of the thickness. That ain't much.
Lots of info on the interweb on re-applying gel. Most is voodoo and not a diy or on the job training thing to attempt. You may have a marine refinish shop near that has the experience and proper equipment. Usually paint application equipment will fail. I can't determine what you should do since your ideas of cost effective solutions have to be dealt with.
I will suggest going forward, that if you end up with a new rv or a new finish on the old one, get yourself some good UV protection and apply it regularly. I use Chemical Guys Jetseal. I only use marine wash products and apply using a soap cannon followed up by a quick scrub using a marine brush on the pole. They're cheap at wally world.
Since you're only 6 or 7 miles from me, PM me if you want me to come look at what you're dealing with.
Good Luck in your choice.
Experience is what you get when you don't get what you want.
2017 White Hawk 30RDS (It's the wife's)
15 years on a Harley with a tent and then life happened.
"We'll be friends until we're old and senile,....then we'll be new friends."