My biggest complaint has not been from hauling rigs.
Its been from hauling my conv't. Its a severe pain in the ass for me to find a trailer to rent that is wide enough for the car and can handle the 5000 load decently. I take it to Homecoming parades and one year I had a freaking construction trailer that weighed more then the car - something you would see a backhoe on behind a dump truck.
Since I tow different types of things, I would really like an enclosed trailer for both security and protection.
The airbag idea sounds pretty cool, and I also agree on multiple tie-down points just for the benefit of being able to handle any situation.