I like the look of that stuff cmd Strax posted, and I bet it's nearly as reflective as Mylar, Panda film is cheap and easy to work with, but you need to use bits of cardboard when you staple or it tears piss easy, Mylar(good Quality stuff) won't tear in the same way...I've been thinking about getting some of that insulation stuff for a Cupboard that has an outside wall, Temps/Humidity is right pain in the Winter months, cupboard Cold(well one Wall) and Lights Hot...Do need to sort it properly once it's not in use..
To OP I'm subbed...Looking Good so far m8
Peace