Put them in the shower when it is that cold outside. It is sort of out of the way, and a place to keep them inside.
If your plan is to refill the fresh water tank from the jerry cans, you might want to add hot water to them before draining it all into the tanks, or fill the jerry can with 130+ hot water from your hot water tank to heat the fresh water tank a little bit. If you only have 20 gallons of fresh water in the tank, and pump 6 of that into the hot water heater, and those 6 gallons back into the tank, and let those 6 hot gallons back into the fresh tank, it will warm it from say 45F to around 60F - 70F.
In this way, you can have a warmer shower, and reduce the risk of freezing the fresh water tank as well.
Good luck!
Glad that you had a great time camping!
Fred.
