I use it on the front window awning including the decal, the doors and the Sunline decal on the back. The awning and doors seem to be "different" than the sides in some way and prone to yellowing. Sunline didn't make the doors and possibly not the window awning either--Jon will know for sure.
I guess I'm just a dumb fan of elbow grease and wax the trailer twice a year--without a buffer. It looks good despite sitting out for more than 5 years and traveling 30,000 mi. I also 303 all plastic like fridge vents, vent lids and AC shroud.
I may start using 303 on the nose above the clearance lights which is at the right angle to the sun to be especially prone to oxidation. I just did some restoration with Protect All Fiberglass Oxidation Remover and Color Restorer and will add a post to that thread in a day or two so you should look for that. Compare our sig photos and you'll notice that the slide out Sunlines have a completely different nose profile than the 2499 and other non-slides and that may make the 2499 types more prone to oxidation above the clearance lights.
2019 F150 3.5L Max Tow
2015 Silverado 1500 NHT
2014 Arctic Fox 22G
2005 Sunline T-2499