Furnace mantainance and inspection.

Do you have a model number and brand? "Heaters" are usually passive, Furnaces have a fan and require 12 volts to operate. A photo would help.

The first thing to do is clean everything. That would be the valve area, under and around the burner chamber, plus the exhaust. Check for nests and debris. You can vacuum and air blow.

Check the gas system. Turn on the tanks and smell inside. Leave the tanks on and sniff again in an hour or so. If you don't smell gas, then light the stove top burner. It may take 45 seconds or so if the trailer hasn't been used in a long time.

Once the propane is "in the system", you can try to light the heater/furnace. It should have a pilot, which you light first. The knob should either push in at the pilot position or there may be a separate red knob. Once pushed in, propane will flow to the pilot. It often takes several tries to light the pilot, pushing the knob all the while. Release the knob after the pilot burns for 45 seconds; it should stay lit. Turn the t'stat up to medium and the start knob to ON. The burner should light.

RV shops are very expensive for this type of work. Get an estimate before requesting any work. Often, today's techs are not trained on vintage appliances and the recommendation may be "you need to replace this". Be aware.

Give us some more info and we can help more.

We were in almost the exact situation. Previous owner said the heater worked, after getting it home and taking heater out, so much rust in the burner box that we decided we didn't want to risk the CO problem. Ordered furnace used on Ebay.