Jared. Have you been to the Beall site. They use a hydro motor and a chain sprocket under the truck box that engages the stinger on the transfer box . On the bottom of the stinger they use chain to grab the sprocket and that how they load the box.
I'm going to use that small winch gearbox with a gear attached and on the transfer box install a rack gear of the same pitch, so basically it's the same thing. With the ratio of the gearbox the only way it's going to move is under power, so i don't think it may fall out. It's a five reduction box and RC rates it for three pound pull so being on the flat with rollers under the box it should transfer quite well.
http://store.rc4wd.com/Replacement-G...nch_p_982.html
I haven't looked for rack material yet, but I do know that it is available in nylon and that should be plenty strong for the job.
Rob