First of all, you should not replace a GFCI Master Receptacle with a standard one. It senses low current leakage between the COMMON and the GROUND wires of the SLAVE GFCI receptacles.
These GFCI receptacles are placed in areas such as the Kitchen and bathrooms for a purpose. If by chance you were to get wet or touch a metal appliance that has a wiring problem they will sense the current and could save your life.
If both AC units are functioning then you have your 220-VAC and your symptoms point to your possibly having wired something improperly.
So in summary; first put the appropriate GFCI Master receptacle in your RV. Second, I assume you mean tht your breakers in your MAIN breaker box have voltage on their OUTPUT LINES?
Third, when you say your secondary breaker box has NO power to all of the breakers in it, then in a standard wiring situation the input wires to this secondary breaker box should be fed by your MAIN should be wired to your MAIN breaker in your MAIN breaker box the same as the ones in the MAIN breaker box.
So, try to trace that wire back to your MAIN box.
I must say at this point that the wiring in an RV does not change unless someone did it, just like I assume your RV did operate properly before your problem. With this said, double check any wiring changes you might have made.