Adco manufactures covers specifically for "pop-up" trailers of all sizes in a number of different fabrics (they also manufacture custom covers to size & make covers for motorhomes, trucks, vans and "normal" travel trailers) - here's a link to their page for covers appropriate for HiLo's: (
https://www.adcoprod.com/Universal-R...iler-RV-Covers). We currently use one of their "Aquashed" covers, but it's not designed for UV protection, so we're probably going to upgrade to a "UV Hydro" for both rain and sun protection.
As far as maintenance on the fiberglass skin goes, I've used Marine 31's boat polishing products with good success (gelcoat is gelcoat, whether it's a boat, dune buggy, or trailer).
Our 2307C was pretty oxidized when we got it - white powder would come off on your hand if you rubbed the end cap surfaces. Attempted to clean and polish by hand and got essentially nowhere, so I broke down and ordered a fiberglass oxidation removal kit from Marine 31 (#7424XP - Porter Cable variable speed buffer with pads, oxidation remover, polish & wax -
https://www.marine31.com/porter-cable-7424xp-boat.html).
Took some labor, but both the molded end caps and sheet fiberglass side skins polished up to an almost-new finish with a good gloss, and the buffer makes keeping it up relatively easy.