I am going to ask again, IS THAT A COMBINATION circuit breaker and GFCI?
Hot tubs are supposed to be either well grounded or protected by a GFCI.
Now: why I ask:
Many trailers do not play well with GFCI's. often it is the converter, Some of them will trip a GFCI if the batteries are low, others will work fine if batteries are low but trip it if they are full up.. I do know why. Some just work fine.
Another trouble spot is the inverter... on my coach for a while I had the inverter wired improperly and it would trip the breaker,, IF, that is, you have an inverter.. I wired it wrong, so I re-wired it correctly, works much better that way.
And in some older RV's the neutral and ground may be bonded, either by accident or design, and that too will bother a GFCI.