Here is a link to Trinity trailers web site.  I don't like what they have done with their web site but I like their trailers.  If you have the proper video/flash player, when you go to the VIDEO link and then the EAGLE BRIDGE® VIDEO, it will show the options available for unloading.

If you are always unloading where there is 240v power, you can opt for an electric motor driven variable displacement pump.  The gasoline engine driven variable displacement pump units are popular around this area - but everyone is apt to want to borrow you trailer.  The engines usually start well, even in cold weather and last pretty well as long as they are kept full of oil.  There is plenty of space on the trailer to carry an extra can of gasoline - unless you just really want it in the sleeper.

I have the wet kit on my truck and like that setup.  I can unload 30 tons of sugar beets in 7-9 minutes if the piler can keep up.  The pony motor units can do about the same.  I prefer the belt trailer over a hopper trailer; I can back in and dump in a stall in less time than it takes to line up an auger to unload the hopper.