I may have to give up also and start to save my pennies toward a paint job.
Believe me, it will shine. Just keep at it. Don't try to do it all at once and don't expect it to shine after one or two coats. Although I posted it before, I think most of it was lost when the forum was hijacked. Just about anything will work IF you keep at it. Especially the first year or two. I really got teased in the beginning, but I don't mind. I only wax it about once a year now and the bugs just wash off after a trip. I do try and smear on a coat of wax on the front right before a trip. I have had more people than I can count tell me that they thought my trailer was new. Not those that know fiberglass trailers, of course ... just those that aren't familiar with them. IMHO, it doesn't look new to me. A brand new one has a surface shine that only new gel coat can achieve. However, mine has a deep patina shine that I just love.
My personal favs (both available at marine stores) are:
Polish (for cleaning and shining dull spots): Starbrite Marine Polish
Wax (for protecting): Meguiars Flagship Premium Marine Wax
NOTE: I really do not recommend a product that does both. At least for long term endurance. Just my opinion.
I cannot begin to tell you how oxidized mine was when I got it. You couldn't touch it without getting chaulk on you. The top gelcoat is so thin in a few places, that I can actually see where it is starting to wear through. Yet, it still shines. When I got it, I really thought the only answer was to have it painted or new gel coat applied. I wasn't having much success in my search, so I started cleaning, polishing and waxing. The rest is history.
Lastly, if there is any way that you can have proper protection over it when not in use, it will go a long way in keeping it like you want once you get it there.
[b]Edit note: See these "Legacy Posts" on restoring the shine ("Old like New (almost)") and "Maintaining the shine".