It sounds like you are a candidate for closed cell spray foam in the lid, though with all the walls being glass I am not sure you will be gaining much. Drapes and ensuring that the sliding glass doors are "air tight" (most apparently leak like sieves) will also help somewhat. Do you have an insulated concrete slab in there? That will act as thermal mass if the sun gets to it, radiating some heat back out at night. BUT, with glass walls, you have a tough row to hoe. If you insulate the roof on the inside w/ foam, make sure whatever the roofing is made of will take the heat, 'cause it is gonna get hot (may need ventilation between the foam and the roofing). Good luck to ya, and don't freeze in that 40 degree "cold".