I had such an enclosure. I took the cover out to the shop and drilled a set of 1 inch holes and then glued some spare window screen material from the inside.
Much cooler now and I feel better about it.
Bob
I have a USB External Enclosure holding a 160 GB Hard Drive. It gets very HOT, not just very warm, but not "burning" either, but very uncomfortable to the touch. This in about three hours of use. There are no ventilation holes on the Case, which makes me think that it should just get warm. Is it normal to get very hot ? Thanks.
christy.

Chowhound
Comic Vine
GameFAQs
GameSpot
Giant Bomb
TechRepublic