I am a year round liveaboard and shrink wrap my upper flybridge to my aft sundeck top. I will not block the windows as radiant heat through them is a huge freebee. Point your bow towards the south to get the most solar time possible. Shrink wrap helps with snow removal and some thermal benefit up top.
Tom - Is that a DIY project? Sounds interesting. We have a mast to contend with in the middle of the upper deck. Do you have any pics?