Some other questions mainly about freezing conditions:
Is this porch heated, enclosed, or not enclosed?
If not enclosed consider wind chill?
How much water line will be exposed between the heater and a heated wall?
In a former residence, my water heater was in an unheated attached garage. I kept the water heater off except just prior to use. One night the temperature went to low teens. I had a pipe freeze and burst behind the water heater.
So if moving the water heater to the porch think about all the ways something can freeze then be prepared.