This is the type of cabinet i used about 6 yrs ago. The floor space was 2x2 and I had 72" of height.
I put 4 2" holes in the floor and L shaped black piping to hide the light from the bottom. the exhaust had a 6" hole with a carbon scrubber attached to it outside in the back. I used foam stripping to hide the light in the doors. The light hung from the ceiling in the cabinet and my favorite part to help with the heat was the heat shield i put on the light, inside the ballast. I used a pyrex baking tube (bought on ebay for $15) and put it over the lamp. I attached the exhaust fan to this light / baking tube combination. It kept the light cool and allowed for two nice plants to grow within 6" of the 400W HPS.
Pyrex Bake Around
The entire unit was on 4 casters and was locked. the lock on the front was the only thing that was odd about this cabinet in my basement. This is the same set up I'm going with again.
I'm here to brush up on my seed banks / strains before i got at it again. I'm considering using a 600w this time, but will really fight heat control. The 400w worked great, however I had a really nice fan. It wasn't the inline kind, i think it was called circular or something. Very quiet, it's the only things I have left over from the old op.