Well, Not a expert on that model trailer....
But, if it is a pilot light model (I doubt it), It would have a knob for turning it on inside the water heater door outside the trailer.
If it's an electronic ignition model (likely) the water heater switch back then was typically inside the coach on the wall in the bathroom. Normally it was a black plastic rectangle about 1 1/2" high X 2 1/2" long with a rocker switch than lit up for a few seconds to tell you the heater was lighting. If the light came on and stayed on, it meant that the heater did not light. Turn switch off, wait two minutes, and try again. After changing propane tanks, it would often take 3 or 4 tries to get propane back to the heater so it would light.