There are a few options with screw drive....for trailers use the screw drive set up that OZ truck showed us...
If you want a 6 wheel dump truck there are a few company's that sell a lift that simply bolts in to the frame (search Carson or lesu ) and you connect it to a low geared motor such is what Carson offers.
Here is a thread I made with the use of a lesu screw lift and Carson motor in a tractor dump truck...
http://www.rctruckandconstruction.co...ead.php?t=7706