If your going to use computer fans, i really like the ones from Thermaltake called smart fans they have a speed adjuster and a sensor so you can keep them on low nice and quiet then when they detect more heat (i think the range is around 68F to 130 F) they ramp up the speed by themsleves.Thier real cheap too like 10 bucks.For a small area they would work just fine.I onced used them in a small wardrobe grow and they did great
as for your closet i would have to agree with the inline fan although if it was quiet enough.