We bought the aluminum foil skinned bubble insulation from Home Depot and cut it to fit inside around the canvas. You're right it does brighten up the interior remarkably. We store it under the mattress.Our last trip was 0 degrees celcius daytime and -5 ish overnight. We use some dollarstore automotive reflective sun shields as the oversize ones tuck into the hardwall and fit snugly to the roof. Using these (15 dollars total for 5), our furnace only runs half the time it would without the insulators. They are reflective both sides and seem to be made of a durable bubblewrap type construction. Our condensation situation went from a morning wipe of walls and roof, to just a wipe in the sleeping compartment. Hope this helps. Sometimes simple is right. My wife bought these for the cab of the truck as that is where we keep our food, coolers and these worked so good to insulate in plus 30 degree C. She suggested them for the cold and we haven't looked back. The reflective on the inside helps with interior lighting as well.