Winterizing Travel Trailer
Hi robsouth,
If you scroll down through the previous posts here, you will probably find all the answers you need.
The short answer is: if the temperature is going to stay below freezing for a long period, I would put nontoxic antifreeze in the plumbing system. If all the water is out, you should not need it, but "if" is the biggest 2-letter word I know of.
The easiest way to get the antifreeze in there is to bypass the waterheater (a permanent bypass kit with valves makes this a 30 second job), pour antifreeze into the fresh water tank, turn on the pump and open each faucet until it runs red. In the spring, flush with plenty of clean water.