[jetskier]

I don't know why you'd need an additional 50A breaker. The shore power circuit at the post should have a 2-pole, 50A breaker protecting it and the trailer has it's 50A breaker internally in the distribution/fuse box. Unless you want to be able to use the 50A breaker before the inverter as a switch, I guess you could mount another small panel with the breaker only.