whoops a typo in my earlier post!
Yes, do check out the "do-it-yourself" thing.
Some enclosures have better ventilation than others and some with metal casing may be more effective than plastic cases.
Unfortunately, HK tends to be warmer than other countries. My laptop seems to be a lot hotter than I'm used to.
Re partitioning. As the drives get bigger the more you're likely to lose something if anything goes wrong. You can use a drive imager to back up a whole partition easier than say, a whole 300GB drive.
Also, for organisation reasons, it may pay to put certain things into partitions rather than folders.