There's a few guys on the hdt section of Escapees that have something like what you're thinking. I've seen them use a winch drawn frame thingy that they put the front tire into a bracket and the whole thing then gets pulled up into the box. I've also seen a beam up top of the box that slides out and a winch then lifts the bike straight up. Then the whole thing slides back in.
Maybe search around here a bit and see what you find:
HDT - Escapees Discussion Forum
'03 Freightliner FL112, 295" wheel base, with '03 United Specialties 26' living quarters, single screw, Cat C12 430 h/p 1650 torque, Eaton 10speed , 3.42 rear axle ratio