Welcome to the forum.
Plenty members on here that will own T40 and see what they recommend.
I’d have thought you’d be looking at a carpeted bunk trailer. Decent makes include Indespension, Snipe, etc. You get what you pay for with trailers in terms of build, tow-ability, quality of galvanising.
Back to storage, what does the off-site storage provider offer in terms of insurance? Speak to a broker such as craftinsure to see if they would cover while at a location which isn’t your home. You’d be covered while it’s in transit and in use which you’ll need.
Speaking of trailers, this is a bit Heath Robinson for my liking!
https://www.ebay.co.uk/itm/175591226...hoCfEcQAvD_BwE