I bought a 20' enclosed (24' total) some years ago to use as a portable garage on race days and at home, work. I'm fairly certain it has 5000 lb torsion axles and it made a trip to Idaho weighing in at 10000lbs. It tows smooth at 85 if you ever get up that high and holds everything. The picture above is glassman (Mike's) Camaro when I picked it up to bring to the shop. His car is a 70 1/2 Camaro and the transmission is laid behind the car on the ground. It has room up front for cabinets (though I've never installed any) or a 18" or 24" deep toolbox. 12" would probably be perfect. It has hauled 48" SnapOn toolboxes with cars without issues. I am really happy with it. Space hasn't been an issue.. especially because I don't need ramps and I'm usually using a truck to haul it.. (the truck bed has room for stuff). The man door in the front is totally useful.
I also have the E-Track running the length of it along the walls. I ought to run it along the floors, but the wall stuff has been more than enough in the last five years.
on a side note, parking this trailer is not always easy.. backing up can be difficult visibility; and parking lots don't always have the space; and getting in and out of gas station pumps would be much harder with a bigger trailer. I wouldn't want a 24 footer for me.