for good passive intakes look up Dark Room Louvers on google. They are used to allow air in dark rooms for phatography. Get one or two 8 in louvers. They will allow no light in. They run for about $20 a shot.
Other than that you are off to a good start.
Adieu
BlueBear Reviewed by BlueBear on . My Grow Cabinet... Almost Done..... This is my grow cabinet it is almost done. Thought I would post it for peeps to see. Dimensions 60 x 30 x 17" (152 x 76 x 43 cm) Top is a T5 2ft Balast 4 bulbs 2000 lummes each 2 warm 2 cool. Bottom Is the HOme depot Route. 27W CFL Plan to have 6 total. Top has a 5 " Computer style fan and the bottom has 2 5" Computer style fans 105Cfm fans. 30bucks each The temps right now stay around the same as the outside of the box. I got real messed up when I didn't make the Air intake hole Rating: 5