Hi. I don’t know your coach at all, or where that control fuse is located, but to clarify I think you are saying that you have a solenoid style (electric) LP gas shut off valve that you can’t turn on manually by remote switches?
If yes, do you know if this LP gas valve solenoid is also tied into the propane detector (per coach manual)? If so, is the propane detector “on” and working OK? If the propane detector is “off” (or failed), it likely also keeps the gas valve “off” and possibly may not be over ridden by manual switches, as a safety. A propane detector control relay likely locks out manual switch control of the LP gas valve (just guessing here).
Have you checked for DC voltage at the LP gas solenoid valve, when someone else operates the switches? Maybe the solenoid valve has failed closed or there is a bad electrical connection(s) ?