Often a breaker can look O.K. when it is actually tripped. Turn off each CB and then turn back on. You say you tested one of the GFI outlets and found no juice. Did you just test with a probe in the outlet or pull the outlet out of the box and test at wire/post connection? A bad GFI might be the problem.
With RV unplugged from shore power, you should remove the cover of the main CB panel and check that all wires are tight to their connection. It is not uncommon for vibration to loosen connections. If it is a 50 amp service, you need to check for loose wires in the transfer switch also if you don't find a loose wire in the CB panel. If it is 30 amp, you'd get no power if wire was loose in the transfer switch.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI