Since you mentioned you have an inverter the unit is likely wired with the power going straight to/from the batteries for the inverter/charger (The inverter is most likley your charger as well)
Things like the salesman switch/battery disconnect are thus turned ON, because if they were not, shore power or not, you'd be in the dark (lights would not work).
It could be bad batteries but I put that low on the list.. I will stick with your choice of overload or bad breaker cycling,
To test for load
you need a DC clamp on ammeter,, Clamp the POSITIVE wire that feeds the coach, or the negative wire that does not go to the inverter, either one will give total amps to the coach.
