Originally Posted by Gene
From the outside door, if you look on the left behind the copper gas line where it meets the gas valve you should see a plastic plug that you unscrew to drain the water heater.
The water will not drain completely and that is ok as the tank is laying on its side and the small amount of water left will freeze up the side of the cylinder with no damage.
However, to be safe, since it's such a cold unpredictable winter, you should open the low point drains to drain as much water out of the lines as possible. Want vintage is your camper? Look under the camper between the skirting and the frame for two stubby pipes. These are the low point drains and the valve to open them will be inside in a cabinet directly above. Turn each valve as far as you can and check that water is coming out. Leave the valves and all taps open to minimize pressure if there is freezing. I would think in TX this should be good, but you can also blow out the lines with an air compressor.
...and you can always run the furnace or small heater. Open the cabinets with plumbing and you'll need very little heat to prevent freezing in TX.