If that is tinfoil, then my first piece of advice is get that stuff out of there, it will create heat spots and burn your plans. Use mylar or paint the sides with glossy white paint, its more reflective and less harmful believe it or not. As for your fan, if that is a computer fan your battery will die pretty quick, here is a post I gave for someone else on how to power a computer fan

"DO ALL OF THIS WITH EVERYTHING UNPLUGGED!!!) <-----DISCLAIMER

Most computer fans are 12v, you can find that on the tiny label on them. They each have a positive and a negative wire, splice these so there is some raw wire showing (usually copper or silver).

Now the other half, the power supply. Like most people, Im betting you have an only phone charger lying around the house. These convert 120v outlets to either 12v (like your fan) or 6v (under the max amount for your fan, so still okay) These as well have one positive wire and one negative wire. hook them directly to your fan but make sure they dont touch so your fan doesnt short out. You should connect one wire, electrical tape it, and then connect the other one and tape it as well, that way you lessen your chances of two active wires touching.

After they are connected, plug it in. It should run perfectly normal and be silent as ever, I am currently running 3 of them off of one phone charger, gotta love it. Have fun"