I bought two drive caddys from ebuyer for only £4.99 each. (
http://www.ebuyer.com/UK/product/99222)
That way you can use any hard drive(s) and swap them over when required although it depends how portable you want them to be.
Because it is in effect an internal drive it is much quicker and should be more reliable. (I wouldn't remove it without switching the PC off first though)