For me, electricity seems a mysterious thing. Having spent the last several days at Acadia Nat'l Park on the Maine coast, ill-prepared as it turns out and mostly freezing, I am thinking about purchasing something to use briefly to warm the sleeping bag before getting in. Is it more efficient to purchase a 12 volt version that can be used only in a vehicle or, now that I have a wonderful inverter installed in the camper, am I better off buying a 110-120 volt model that I could in the house as well? My plan is not to fall asleep with it running, but rather to make the leap into the sleeping bag less abhorrent. It's not fun jumping into an icy lake which is how it feels now.