I'm going to dig my crane out today so I can start thinking about it again, if I come up with any ideas, I'll post them up. A fereind of mine has a portable crane that he got from a hospital(they use it to pick up patients), the wheels were broken and they were throwing it out. The whole thing weighs less than 35 lbs, and it rated fro 500 lbs lift. Its all made with tubing and uses a slim cylinder, its perfect for hanging outdrives

Crane
 

You could brace it to a gooseneck ball or a fifth wheel hitch.