Have the Xtreme heater in my boat in north Atlanta. It hurts the pocket, but is worth it in my case were the temp goes from 18 to 65 in a week. That way I can hit the lake still. I just drain the manifolds, plug in the heater and go home.
I installed an Xtreme heater in my bilge last year and they work great!
These Xtreme heaters are so small I put a 600 w under each engine