When I was an over the road driver I always used a queen size quilt to keep warm. The extra width allows you to snuggle in and bunch the sides around you and keep warmer. When not in use I would roll the back of it up against the back of the bunk like a bolster pillow. They also make 12 volt pads that are heated that you put under your sheet and sleep on top of they do not make much of a drain on your battery.