1 leg of my electricity is dead

[Bob and Jeannette]

We were in the RV when we heard a beep which turned out to be the refrigerator power going off. Closer inspection found that 1 side of the breaker box was not working. I turned off every breaker and powered them back on, no help. The plug was very oxidized so I sanded it with 1500 grit until it shined, no help. I put a meter on the pedestal and assuming top and bottom are neutral and ground I got plus 120 on on each side connector from ground. Moved my power cord reel half way, no help.

I am not sure how to proceed in best way on my Montana. Do I just empty the basement and start pulling off the side panels or is there something else that I could do first to save time and embarrassment?