Have a look for one of those trailers that sit flat on the ground to load and then rise up to normal ride height. You could probably modify yours to do that.
This is the type I am thinking of. Might be worth while to ring them and ask if you could just buy the axel/lowering bit to put under your trailer. http://www.ebay.com.au/itm/Raceking...amps-or-tilting-RACE-DRIFT-DRAG-/121774668871 Or this one using air pressure. Or hydraulics.