The fresh water holding tank was the most vulnerable in our Bounder. We used to put a droplight in that compartment when we found ourselves in really cold weather. I think because of that, I automatically went to that with the TM . . .
Anyway, we are going to install a vent grill for the fresh water holding tank and won't think about that anymore.
We've already used Digger's advice with the Thetford and think that is a terrific plan.
Today we installed an Ultra Heat tank heater on the grey water tank.
http://www.ultraheat.com/shop/Tank_H...nk_Heater.html We couldn't follow all of the installation instructions because the TM holding tank is shaped funny and doesn't have a flat bottom. We thought we'd give it a shot though and will let everyone know if it is still attached when we get back from Southern California.
Malinda