the vehicle uhaul wants to inspect it the tow rig, not the towed rig. uhaul has never laid eyes on any rig I've towed.
Uhaul dollys don't have brakes (at least none that I've seen). but you can buy a dolly with brakes.
wait, are you planning on pulling the one MJ with the other MJ? I'm sure it's been done, but that sounds kinda sketchy to my ears for such a long way over the rockies.