Bad GFI? You just need one GFI unless you have two phases in your camper. All other outlets should run after the GFI. About $10 for a new one.
AC is on another circuit, unrelated, so if both then you likely have no power coming in.
Get a multi meter, also about $10. You can test to see if there is current, sometimes there will be less current, too little to run anything, but enough to see that something is happening. is a great tool to start looking at electrical issues. Anyone can use it.
Check to see no circuits are tripped.
Unplug from electrical and check that all the wires seem to be fastened tightly. remove circuit breaker cover and just look around.
look for corrosion.
Look for broken wires on you extension cord. very common for wires to break right at the plug. New bolt on plugs, also about $10. You might have to unscrew the plug or just assume it is bad and replace it and see if it works. Start with the cheap things. Not a bad upgrade either to have a new plug.