I'd guess at a minimum it will have the FTP capability of the WFT units that include ethernet, so you could use an SSD in a netbook or laptop. Either that or load up a NAS appliance with some SSD drives, most need mains power but not a lot of current so you could use a small inverter.
A number of small NAS appliances usee "cable wart" power connectors. For instance, the external power supplies of my Synology NASes provide 12V to the NAS itself. The DS410 (which I have) uses 20W on standby and 60W (or thereabouts) with 4 3.5" drives spinning. It can also accept 2.5" drives, which should allow you to use SSDs. The DS411 (which replaces the DS410) uses 10W on standby. The DS410 is hardly a high end NAS, but I have still managed write speeds of over 50Mbytes/sec - this may be a challenge. (I can't remember exact numbers.)
It may be worth investigating a hack to just run a NAS off 12V supply, cutting out the manufacturer-supplied power supply. I think Synology also has NAS that is designed to take just 2.5" drives. You may need to check on performance though.
You should probably be able to achieve the same with other manufacturers' NASes.