i think what you need to do is just leave veg for the cfl's. you dont need the hps too until flowering. the cfl's will be fine for the first 3 weeks, this is also better because once you switch them into flowering its good to have a big boost in lumens/wattage, it helps your plants a lot. what you need to do is look up the rasta fan on the forums and just use one of those, i can give you the baisics of how it works-
1: take a regular fan u have lying arround and put a trash bag over it
2: tape the bag to the base of the fan so that it is sealed
3: cut one hole in the front of the fan and one in the back so that you can get a duct to fit inside the hole on each side.
4: have the duct that is going to the fan somewhere that is fairly cool and have the duct going away from the fan going into the box (best if the intake duct is somewhere outside or on a window, fresh air is good)
5: cut a hole in your box to allow outtake

you baisicaly just need to customise this design to your needs and what you want to do. this should help some...

you could also just cut a hole in the top of your box so that the hot air has a place to go and put a fan underneath to help it along.

vegging for 3 weeks might be a little much in that litte box. ive never grown nl (or any other strain before) but if it stretches too much your gonna have a very crispy plant when it reaches that 400 watt hps you got.

good luck :thumbsup: