lows below freezing, bad idea to camp?

Shouldn't have a problem with water freezing at those temps. Make sure your propane tanks are full and run the generator a couple of hours each day and you should be fine. I don't like the idea of combustion inside the TT. Condensation is an issue and if you leave the windows open to make it safe you loose the heat. Use your furnace, that's what it's for. Especially with little ones.