If yours has the original equipment. I doubt that it has "auto" light.
The furnace has a "standing" pilot that you have to light by hand. There should be instructions on the door or side of it as to how to start. You need to check out the plenum and combustion chamber on these old units; it could be rusted out and be a real death trap.
I've attached some photos of my refer with the operating procedure. There are a couple of ways to go about it. From the front (top photo) and from the outside (2nd and 3rd photo) if you can't make it happen from the front. In one photo, I'm holding the valve open and in the other I'm lighting the pilot. The refer must be level to work. Put a level on the floor of the freezer and check it in both directions. Level the trailer accordingly. Don't use the levels on the outside of the trailer, they are not accurate enough.
The water heater (bottom photo) has a standing pilot. There will be a knob with 3 positions. "OFF-PILOT-ON" , the blue one next to the red one in the bottom photo. To light the pilot, put it (the blue knob)in the pilot position and push the red knob in while you light the pilot. Keep the knob in to get the thermo couple hot enough to open the gas valve. Meaning the pilot stays lit after you release the red knob. Once the pilot is lit, rotate the gas valve to the "ON" position. DO NOT light the water heater if it is not full of water.
Start by turning the valve on top of the tank to open. Then follow the gas lines under the trailer with a spray bottle of soapy water; spray every joint and fitting on all lines and look for soap bubbles, if there are bubbles you have a leak that needs attention.. There will be branch lines off of the main line to each appliance; each of these branch lines (check these lines for leaks as well all the way to where they enter the appliance) will have a valve to shut the gas off to each appliance. Because the lines will be full of air it will take time to purge the air. Start with the stove top. Open the outside valve under the trailer that feeds the stove. Then turn on one of the top burners, listen for the hiss of gas; if you hear it start trying to light the burner with your BBQ lighter. Once lit, leave it burning for a few minutes to purge the line of air. In the mean time you can light the remainder of the stove top burners. Some stoves have a valve under the lid to turn on the gas.
Again; it will take quite a while to purge the air from the lines, especially to the refer and water heater since the pilots don't consume much gas. So have patience.
Knowledge: "A gift to be shared. A treasure to receive."