Are you talking of shrinkwrap over the top of the boat as a cover or something inside the boat?
I haven't done this but thought it would be worth considering: There is electric 'tape' used on the overhangs of house roofs to melt the ice dams. You could fish this under the floors to add heat under foot and keep these areas warm. They are wired for 110v. I suspect they are 10 to 15 amps draw.