Originally Posted by khyberkitsune
Wow that's going to be a TON of heat in the box. Yes, get the ballast outside of the box. Beef up your cooling, if you're going HID you should stick with the 400w, get a cooltube for that bad boy, put it in the center, hanging vertically. 8 plants, one per square foot, on the outsides. You won't even need the side CFL lighting with that configuration. 600w would not be necessary. Try using MH for this, if you can, since they're more often used in a vertical orientation. This method will get you far more yield than you would by using an overhead horizontally-oriented/reflector light setup of the same wattage.
You could also try LED, but that's only if you've got the setup cash. Two 120 or 150w panels would do the same thing, and with the way those work, this can give you an option of making two tiers in your cabinet, and doubling your plant amount, and giving you tons more options in your preferred method (you could run a mom/clone/veg cabinet down below and flower up top, for example.)
Different approaches will yield different results. Just tossing in some ideas. :)