NatanColenberg:
i quickly run out of SD card space.
Given the large capacity and small physical size of an SD card, I'd have thought that simply taking more SD cards with you would be the most sensible option. Even if you fill up an SD card per day and stay away for months, this is probably going to end up smaller and lighter than any HD-based solution you could devise by the time you consider the disk itself, and the controller, card reader, power supply, cables ...