First some bad news...
I have a very very similar trailer to yours. I have a 2004 R-Vision 30QBSS and the gas water heater is not ideal.
There is NO switch inside, NO breaker inside, NO electricity required to run the water heater. You need to go outside and physically open the water heater access cover. Assuming that you have already filled the water heater with water (do you know where the bypass is located?) and have turned on the propane at the tank(s)then your next step is to light the pilot.
Turn the gas valve knob to pilot, depress the knob, and hold a flame at the pilot tip. A BBQ lighter works best for this. After the pilot ignites you need to continue holding down that knob for about 30 seconds. Release the knob, if the pilot stays lit, turn the knob to ON and the main burner will ignite. After the water temperature reaches setpoint the main flame will turn off and the pilot will stay on. Every time the temperature drops, the main flame will ignite to keep it warm. You will be using propane the entire time.
If you are concerned about propane use...
You can either turn on the water heater 1/2 hour before you need hot water and then turn it off again.
or
Install a HottRod electric element heater kit (this is what I do) but will require shore power to run it.
Having this type of water heater has an advantage, it does not require battery power to run, but if you are on shore power anyway, it is a slightly annoying setup.
Good Luck!