We did have an intermittent short in our brakes also. After a "not so fun" trip from Southern Wisconisn till I found an RV service place just outside of St. Louis, we finally got it fixed.
After a number of other "troubleshooting" tries, which included rewiring almost all the way from the hitchpin to the brake drums, the service tech pulled the wheels. The first wheel pulled showed the problem. The wires going to the electromagnet were not secured in the little clip that is supposed to hold them in place. This allowed the wires to rub on the inside of the drum, finally rubbing off the insulation and creating a short when the now bare wire would touch the drum. He put in a new magnet and wires, and "voila!" the problem was fixed.
By the way, the dealer was BYERLY"S in Eureka, MO. They do not sell Montana's but do sell other Keystone products. They found a way to take us in even though we were just passing through, and got us on our way. The service tech, SEAN, was as accomodating as anyone could be. They were also able to get the cost of repair covered by the axle manufacturer. I heartily endorse Byerly's as a customer-oriented dealer and take every opportunity I can to stop there and purchase something when I pass through.