Just thinking aloud, really. My little Morris Minor needs wrapping up safely during the winter, and spent last winter on a trailer, with everything wrapped up neatly in a (plastic) tarpaulin. That worked well, but does not really allow for occasional winter use. Unwrapping and rewrapping is a fairly major task, and I do worry about trapping moisture, and chaffing.
A proper garage is not an option, for a variety of reasons, so I thought vaguely about building a shed on the trailer. Yes, it will mean that the trailer stops being a useful trailer, but if the Minor breaks down, the AA can bring it home.
Thoughts are to use 2 by 2 uprights, with ply sides, apex roof, and plenty of preservative. Remove the trailer wheels, and let it sit on the stabilisers - the slope up is about seven inches. This is for occasional, not daily use, so not a major problem.
Any major problems I haven't foreseen?