Thanks for all the really good, quick help. You confirmed what I thought I would need to do - Looks like I should run that furnace to keep warm air flowing into the underbelly area.
I just spent some time reading at the Heartland Owners forum. I have switch controlled 120 volt heaters on all 3 tanks and, as several have stated, I need to keep some liquid in all of them if I turn on the switch for the heaters. Thank You DianneOK - I'll keep water in the fresh water tank even if running off of city water. I will be hooked to shore power.
Lakeside013104 - You may want to contact customer service at Heartland.
- As part of the Yeti package, there is also supposed to be a 12 volt heat tape on the line running from the fresh water tank to the water pump. This heat tape is thermostatically controlled and does not have a switch. It will automatically come on when the temp drops which will put a pretty big drain on your battery if not plugged in to shore power. Turning the main battery switch to 'off' or puling a fuse is supposedly the only way to turn it off.
Again, thanks everyone for all the help.
Tim