Cooltube ventilation question

I'm planning on putting a cooltube in my cabinet that I am constructing and wonder what is the best way to hook up the ventilation.

Will be using a 250 MH/HPS

1. Scrubber => Duct => Light => Duct => Utility Cabinet with a 6" S&P TD-150 exhausting the air.

2. Sealed ducting for just the cooltube with a computer fan on one end.

My cabinet is in 2 sections:
Flowering:
- 34" Wide
- 22" Deep
- 38" High

Utility/Veg/Mother:
- 17.5" Wide
- 16.5" Deep
- 38" High

Any help would be greatly appreciated.

i have a 150w hps in a cool tube i made my self . i plan to have cold air blown in from a pc fan with ducting to and from the tube all sealed in and out of fridge i am converting