Check out the Seacycle unit at http://www.seacycle.biz/driveunit.html
Believe it or not, I designed this unit (Very sim.) about 16 years ago but never built because of cost. I obviously only looked at cats for a market . If your distance to go is not terribly far this is lightweight and could probably be mounted off the front cross beam and tucked under the tramp when not in use. Just a thought.

Clayton
S27, H16