Weston.....no wonder you are "bummed"...... sorry......Crow humor.
First....it would give a clue to know the make of your WH. And, your RV. (Go to your User CP and put it in your signarure)
OK.... does your gas range, fridge, genny or furnace operate correctly? If not, it could be low fuel, no fuel or a diff regulator. If the range works and you try to run another appliance and the range snuffs and goes out.....look to the regulator.
If all that works and you have not used the WH in awhile, the LP just needs a couple cycles to move up to the burner.....most likely.
OK so far.... late model Suburbans and maybe others have that fail safe ignition. If it doesn't fire after 3-4 attempts it shuts down to allow any LP fumes to dissipate. So....
Turn LP off; turn WH off, turn coach master electrical off. WAIT 5 minutes. Master ON; LP ON, WH ON.
Suburbans have a "chip" with that delay program. You need to "reboot" the WH to get it to fire up.
Is your WH LP and electric? Some are. The work around is to fire using shore power or the genny. Actually, if in a hurry....use both. Or save LP when on shore power using electric heat.
Hope this helps....