Another couple tips:

1. You will reflect WAY more light in there if you paint the inside of the box flat white, at least two coats. White reflects more of the light spectrum rather than the mid-range visible light that a silver mirror or foil will reflect. I know it seems like foil is great but for many reasons, it's not. If you can do mylar walls that's fine but flat white paint is even better at reflecting light and not heat.

2. Don't underestimate air flow needs.
You can make your passive inlet vents at the floor by cutting a wide "U" shape at the bottom with a razor and pull the flap out as a slight light barrier. Then if you mount a false floor (like a shelf almost the width and depth of the chamber on a couple boxes) about 6" above the actual floor you reduce even more chance for light to get in. Then you just need to build a simple inlet tube with cardboard and tape to direct the top fan's light away from the girls. You still will want the box to be in a light free environment for budding but it will help by blocking out other light pollution that you may not even notice.

And if you come in here asking why your plants won't bud or why they wilt and don't seem to grow I will direct you right back here to this thread.

Haha....good luck. Keep the progress pics coming.