Heat is one of the main factors which causes HDD to die in most cases.
That is why you should keep it cool as much as possible.The cheapest way for you to do that would be to get dual fans cooling attachement for your HDD such as this one:
http://dx.com/p/dual-fans-hard-drive-cooling-attachment-5152
When HDD is being used for few hours or more,it gets VERY hot.Sometimes it's so hot that you cannot even hold your finger on it of how hot it is.That is one of the main reasons why HDD dies in most cases.So I definetely recommend you to buy and use this dual fans cooling attachement I gave you a link for above.It's only 3.95 dollars and the shipping is free for worldwide.
That dual fans cooling attachement will keep your HDD a lot cooler and extend HDD life a lot.
Of course take note that hard disk drives can die for many other reasons too.Heat is just one of them.
I for example cool my hard disk drive from 4 sides using 6 fans.TOP,BOTTOM,LEFT,RIGHT.