Towing too fast maybe?
True story: Earlier this year we were passed by a newer Dodge 3500 DRW truck towing what looked like about a 17' R-POD TT. Plenty of towing overkill. We were towing our 5'er and our speed was about 60 MPH. The Dodge/R-POD rig passed us easilly doing 80+ MPH...buddy I mean this rig was slap flat movin-on-down the road!!! There were about 6 cars following the rig in line using the rig as a blocker if there were cops ahead with a speed trap. I commented to my wife at the time, "That won't last long". Sure enough, about 3 hours later we passed the Dodge/R-POD rig sitting at an off ramp on the road shoulder sporting two shreaded trailer tires with skid marks leading off the interstate highway indicating two locked trailer wheels. I'm guessing those little tires and wheels and bearings just couldn't take the heat and the speed any longer and finally siezed. JMHO.
Happy camping!!! See y'all down the road!!!:)