Dawn and Hot water, throw 5 gallons of hot water in the bilge and about 3 oz. of dawn and go for a drive (on the trailer, don't push that shit into the waterways).
Once it has sloshed around for a few, drain the hull into a drain pan and let the water evaporate off...
Then grab the simple green and a hose and finish up, should be very little oil left in there.
GT