I just got a neat little external enclosure from OWC that is entirely made of plastic and has no heat sink at all. It does have some tiny ventilation holes but not enough for any serious air circulation. I haven't had it long enough to draw any conclusions about drive life, but it works well and costs less that $20.
If you're referring to their On-The-Go enclosure, I've had one since September 2012 with a Seagate 320 GB drive in it, and can confirm that heat is not an issue. Not even close.
And, of course, there is the bonus of it being so funky looking.
