Don't do it. We've been gone for almost 3 months. We've used 4 30# tanks of propane. It got down to 34 degrees twice. We came inside tonight and had to close the windows as it was down to 74 degrees inside. All is not rosy when you feel a chill at 74 degrees. We set the furnace so it comes on at about 62 in case it gets cold inside.
We did 2 months last yr and 3 this yr now talking about 4 months for next yr. The snow had just about melted at home and today they got another 2". We leave on the 28th, what are we going to do if there is still white stuff on the ground?