From my limited experience, you will want an enclosed trailer to have some extra room, both so you can get around the rhino to strap it down and for the geometry of the straps. My stock rhino is about 55 inches wide, yours may vary depending on your wheels and tires (and any modifications) it is also about 10 feet long, but it is way too big for a 5' x 10' trailer to work. You want your straps to have strength to resist the rhino wanting to move forward and back as much or more than side to side. If your trailer is too short the straps will run mostly sideways, and I prefer mostly front and back.
Some enclosed trailers have doors tord the front as well as the ramp in the back. This is nice as it allows you to get to the front without having to open the ramp (and maybe move the rhino out). The ramp in the back is also a nice feature, if I was going to buy an enclosed trailer I would not get one without the ramp in the back. The rhino is not that heavy, so you have pretty good flexibility, but another option I like trailer brakes. I would look for the surge brake, where the brake is activated by the pressure of the trailer tongue pushing against the hitch on the tow vehicle. This way you have the benefit of trailer brakes even if your tow vehicle is not equipped for trailer brakes.