If your trailer has one of those breakaway e-brake setups couldn't you pull the cable out when loading and put it back when your done? I was leaving a motel one day in Atlanta when this elderly gent was having trouble with his trailer. He had unhooked it to park for the evening and when he went to hook it back up he didn't have it coupled properly and pulled out and the trailer came unhooked. I went over to help him get it reattached and was ready to leave and he came over and said his rig wouldn't move at all. He had pulled the e-brake cable out and when I put it back in for him the truck was running and it was still in gear. Here I am between his truck and trailer and the whole thing took of almost running me over. Fortunately I had the presence of mind to snatch the cable out stopping the whole rig. I had no idea he had left it in gear when he had gotten out to see why he wasn't moving. I almost had a real bad day!
John
John