If it is only happening when you tow I would suspect a connection somewhere that is allowing a hot wire to short to ground. I would find a different dealer and have it fixed under warranty. I would also try to track down EVERYTHING that is on the circuit and keep an eye on it. On my Coleman there were a couple of circuits that were crossed up and backfed from another circuit. I did find one, the other I never did.
In your case it could be caused by a nail or screw piercing the wire, a misconnection, a wire pinched somewhere and the list goes on. Unfortunately they throw these things together and it makes it very difficult to trouble shoot effectively. Basically you have to isolate each item and test the circuit for continuity. The fact it only happens when you tow complicates it even more, it means it is an intermittent problem