The problem with plywood is getting in from here to there. It's heavy and getting a good grip is difficult...especially if you have to carry it for any length of time. An easy solution is to take a couple of C-clamps and tighten them on to each end. This will give you the handle you need to get a good, solid grip.
Winterize your home to extend the life of your fuel supply. Insulate walls and attic. Caulk and weather-strip doors and windows. Install storm windows or cover windows with plastic.