I don't think reverse polarity would trip the shorepower breaker. It certainly would if the ground was in the wrong place, as ground and neutral are connected on shore if you follow it back far enough.
The switch would work if after the main breaker.
As long as the main is a double breaker that switches both hot and neutral there shouldn't be a problem I don't think. Now if the main only switches the hot as in some older boats that could be a problem. In that case if there is reverse polarity and the switch is turned off every circuit is still hot.
Living aboard in Victoria Harbour