Andy i rescently did the same as you but both wheels caught fire and we were on the m6. just picked boat up from having covers made, and i can only assume that the ring holding the breakaway cable was snagged.
of we went and i thought the brakes felt a bit stiff, but big 3.7 jeep had no problems pulling it, to this day i dont know why i didnt stop to check.just thought the brakes were binding a bit. towed for 6 mile and just got on the m6 so down went the pedal, and a big artic was frantically flashing from behind.
looked in the mirror and flames were belting out from both wheels. the wheels were cherry red. the lorry driver was tipping his drinking water on the wheels but they kept igniting.Had visions of the tubes melting. luckilly there was a canal runnuing along the motorway, so many trips back and forth with a bucket finnally had the wheels cooling down.A cop car went past but never stopped. but as we made way later on, he pulled me up for going to slow.next day went down to sbs and bought a complete new 1500kg axle.
it was cheaper than buying the seperate drums bearings cables and wheels.
Another check now before starting of is making sure theres plenty of slack on the breakaway cable.