If a Suburban water heater, it's probably the dual powered propane/electric heating element kind. You can usually use the electric if the propane side isn't working, or vice versa.
If you turned on the switch for the propane Direct Spark Ignitor inside your RV, and the propane didn't light after three failed attempts, it automatically locked itself out. You have to turn off the switch, wait a little, then turn it back on to restart the process.
This link below may help you understand, as well as where the electric heating element switch is located.
BEFORE YOU DO ANYTHING ELSE: verify that there is indeed water inside the water heater. You need to go outside and open the pressure relief valve on the top of the water heater, and see if water comes out. It may be hot so don't put yourself in a position to burn yourself.
Suburban's electric switch and much more
EDIT: Here is a pic showing where the pressure relief is located on the heater.