We always have our trailer undercover 24/7, but with our ROO we also used an Adco we'd bought the first year, before building the cover. It does keep it clean and protect the decals, especially, from sun damage. With our TT, it is also undercover 24/7 and we have not bought the cover yet....mainly because other money drains keep popping up. The only places that have any sun exposure are the back and street side and we're even considering mods to the Rockyport rather than getting the cover.
I'd probably not enjoy dealing with covering after every trip, but for the winter, yes. It's not a hard job, maybe 30 min or so, but DH has that high tech hip and some foot/leg issues on the other leg, so he's not crazy about climbing the ladder to get on top of Rocky. If it were sitting out even through the TN winter it would definitely have an appropriate trailer cover, not a tarp which is not breathable and can cause scuffs.