Hi; A good portion of the heat is lost thru the roof. What i do, in
order to slow this process down is to open the bed upstairs all the way.
Then close the roof up. You will notice that their is only a space left
about 19 inches by 48 inches. For this area i made a plug that fits up
in there. Start with a 1/4 inch piece of plywood. Get that to lay on the
roof towards the front. Notch around the latch and rest the back of the
plywood on the bed. After you get that to fit, get your self a piece of
foam. About 1 1/2 inches thick. Cut this to fit as snug as possible then
glue it to the plywood. You should now have an 1 1/2 of insulation  over
your head. It cuts down on some head room when your moving around in
there but the benefit far out weighs the loss of head room. E-mail me if
you need some pics