You are going to regret the electric heater. The temp difference between inside and outside air is going to create a lot of moisture on the walls and windows. Get yourself a dehumidifier, plug it in and set it for a comfortable 40% humidity level and close things up. When you get ready to go, no more damp bedding, soggy paper products, just plane comfort. BT,DT and the dehumidifier is the best thing I have done for comfort and peace of mind in the inside of our fiver after a wet winter. And yes, we are in the Portland area, so humidity is an issue here just like Seattle.