All the gas appliances in your trailer (stove, oven, furnace, water heater, refer) had a gas shut-off valve connected to them when the trailer left the factory. The heater shown in your picture should, too. If it does, make sure it's on.
Checking those valves is simple: if the handle is at right angles to the pipe, it's off. When the handle is aligned with the pipe, it's on.
Beyond that, I can't help you with your particular heater, it's an after-market type. Did your PO not leave you with all the books for your appliances?
Warning: the following is pure guesswork. Proceed with major caution! Now, if I had to guess, I would start by looking for where you light the pilot. Lighting a pilot usually involves holding a knob or button in a particular position for 15-30 seconds, after lighting the pilot, then releasing it.
One of those knobs should be temperature, why don't you post what the other says on it?
If it's to be, it's up to me.