I did a post on this recently when I found a solution for myself. It uses an android phone or tab and inexpensive usb thumb drives. Capacity is only limited by the number of drives you want to buy.
Worked brilliantly during a recent Scandinavian trip when I ended up with around 80gb of raws to back up on the go.
http://www.iceinspace.com.au/forum/s...d.php?t=102619