removing dull haze from fiberglass?

Elbow Grease is the answer .
I am a car guy active in a car club .
The best solution is FREQUENT washing and waxing over time .
The brand is not as important as the effort .
I use lots of MeGuiars products because they put on a clinic every two years for our car club .
I would not use an aggressive rubbing compound .
The CLAY BAR process is good for removing the road grime that is imbedded .
After that a waxing every month will give you the result that you seek .
A cleaner / wax from any of the readily available brands will do the trick .
I wash my trailer after EVERY trip without exception .
Nothing matches a Frequent washing and waxing for keeping your trailer / car / truck looking new .

Maguires marine One Step compound applied with their orbital buffer (or the Porter Cable equivalent) will work perfectly for your condition. Had a 26' boat from 1985 that it worked flawlessly. Follow up with their marine wax, and you'll be good to go.

Rejex products are very good. Best shine we ever had and lasts the longest in the FL sun.

On my boats and my gel coated TT I use 3 mm fiberglass Restorer.A very simple method for inspection prior to rejuvenating is to wipe a small area with acetone, this will show you what it will look like when you are done buffing and wax application.For wax I use Collinite Fleetwax.It will last 2 yrs here in the desert.

Starbrite Marine Polish - available at most places that have boat supplies. An orbital buffer will help ease the muscle work. Have used it for many years on both boats and trailers.

I used a product called "Buff Magic". You can find it on the internet. Get yourself a 4 or 6" buffer and get to work. I got mine at Home Depot. Use very little on the buffer pad and really work it in. And then just wiper off haze.

When we had our fiberglass cruiser I bought a gallon of Thetford RV Wax that worked really well. It restores and waxes. It also shinned up the boat trailer. I got it at Camping World and would recommend it..

Try a good cleaner wax first. Mequire's will do a good job. But it is going to take some elbow grease. If that does not work. THEN do the buffing polish.

ProtectAll Oxidation Remover. It is made for exactly your situation.

ProtectAll Oxidation Remover

First,do not use rubbing compound, use polishing compound.
TR-3 also does a good job of removing oxidation. Most auto parts stores carry both.