You've checked everything I can think of. Perhaps the switch is bad, but I doubt that. There either has to be a fuse or breaker you've missed or have not found...or...
There is one long shot...on a previous coach that we owned, we had a couple switches and plugs that would not work. I checked everything as you did. I stumbled on the solution...the GFCI button on the outlet at the bath room sink had popped. Unknowingly, this GFC plug controlled several other items.
Like I said, Loooong shot!