Definitely sounds like you lost a leg of the 50 amp power. Problem is where? Multiple possibilities -
1. Camp ground breaker
2. Camp ground power outlet
3. Your power cord
4. Your shore power/generator transfer switch
5. Your coach wiring to breaker panel
6. Your coach 50 amp breaker and panel
First thing to try is your generator. If power is restored with the generator running you just eliminated 1/2 the list starting at part of the transfer switch (#4) and working going down on the list. The switch could still be the problem but you know it will pass the generator power. Another easy try is if you have a surge protector on the end of the power cord. Try plugging in without it.
Going deeper you digging into 120VAC power distribution and if your skills are not up to it I would advise calling for an assist. Many camp grounds keep phone numbers for mobile techs in the area. Getting bit by 120VAC will not make for a pleasant camp trip.
Good luck and tell us what you find.