I've been researching the hell out of this. Most newer enclosed trailers have a 8' wide door opening, but the height is usually just over 6'.
Not for sure yet, but looks like I'm going to have a custom trailer built for me (unless I can find a used one that suits my needs). I'm in the process of selling my house and my wife and I are going to be living on the road where ever my work takes me. This will serve as my mobile garage to hold all my toys, including: My ZR2, 2 quads, 4 kayaks, 2 mountain bikes, 1 road bike, 1 motorcycle, my toolbox, several totes full of gear for hiking, camping, skiing, kayaking, quad riding, etc. I'm envisioning something like 8.5x32 with an extra 18" of height.