Breakers such as this trip for one of two
reasons.......1. Faulty Breaker 2.Overload
From your discussion, I suspect a faulty
breaker.......change it again. If it's not
that, you have an intermittant short circuit.
When the short occurs, the breaker trips.
Try turning off all but one IN THE RV
circuit breakers, and see if you can
find WHICH circuit is causing the problem.
Another thought......if NO IN THE RV breakers
trip, the problem may be in the supply plug,
cord, or connection to the R V......again,
an intermittant short.