Why not just get an enclosed trailer? Such as this.
Off on a slightly different tack, but relevent I hope and maybe worth a thought..................I thought long and hard about this option also, but decided to go down the route of doing away with my trailers altogether, sold my pickup and opted to go for a large van instead. Decided, after many hours on-line searching options, to go for a long wheel base VW Transporter Luton and delighted with it. It can take my Ransomes 728 ride-on and all my other gear that I need for my daily work. Iv'e hated faffing around with trailers for some time now and after going for the large van option. I sill have my Convoy 400 and use this for my smaller site work days and it's all worked out I'm glad to say and I think I made the right decision for my business.
Ifor William call them "Canopies" I had one for my GD84. I realy wouldn't keep your kit in it overnight - completely insecure. I think you will find it restricts your use of the traier - having to end load everything rather than chucking it in over the sides!