External Firewire/USB2 Enclosure vs Internal Array

[amp88]

I'm looking at building a new system round the new year and I'm trying to decide whether to have an internal array with a controller card or buy an external enclosure. For the drives I'm looking at getting 8 of these and with the internal array I'd probably get an Adaptec 3805 RAID controller. I plan on having a RAID5 configuration. I haven't had a good look for external enclosures yet, but the price difference shouldn't be too much between the two solutions.

Am I right to be worried that having the internal array could create too much heat or will it not be a problem? Looking at getting an Antec P180/182 case.

Thanks in advance.