kyotesue - I reread your posting of 3/16/05 and concluded that the dealer winterized the unit and then you bought it, filled the tanks and drove it home. It might be a little risky to not do anything if it gets down to 25 degrees. I don't really know how cold it has to get before water freezes solid and breaks things. At 32 degrees it gets slushy. If it gets cold enough and breaks lines and cracks the water heater - you have big trouble.
You could follow TonyTiger's advice and put in an electric heater for those 1 or 2 nights when it gets that cold. I think he also added the pink RV antifreeze which might not be necessary with added heat.
Alternately, could drain the water heater and blow the lines as Cowboy66 suggests. This is not a major job. You can buy the simple adapter for an air line that screws in to the water fill connection. Just remember to keep at least one faucet open at all times. You can rupture water lines with frozen water or high pressure air.