[ubuntu] installing ubuntu to a portable hard drive

So I have done several installations now of ubuntu . Every installation I do, it is only a matter of time until I'll get odd boot errors or no boot at all. The hard drive is in fine condition in a usb to nb sata caddy. Last time I got 'too small boot block' before an ext4 fs failure. I guess what my question is: how should I go about installing my boot loaders next time? Take in mind I am using this on school computers with windows 7 enterprise installs. Preferably i386 @ all times.

Thanks!