I had this same issue with my toy hauler. My back bed does not go all the way up to the ceiling, the rear of the cage was 5 inches too high. I thought I could flatten the tires and ratchet strap the the rear end to get the clearance, boy was I wrong. I could not get the suspension to load up with a ratchet strap, it was too stiff. Thankfully I was able to put spacers under the back side of the bed frame in the trailer to get the clearance I needed. Is it just the rear of the cage that does not clear the door frame? Maybe try ATV size wheel/tire combo to transport?