If you aren't needing to store more than 64GB of material then you could substitute "thumb drive" or "CF/SD card and reader" for portable USB drive ... solid state media will be 'safer' for long-term storage but obviously afford less space-per-dollar.
Negative. NAND flash w/o active management is NOT a "safe" storage medium, especially in larger sizes of MLC flash.
NAND cells love to flip bits/etc. just for the fun of it. Unless you have some active process to continually check bits and verify they haven't changed, I would not trust it for long term storage.
It's true that NAND is non-volatile and will store electrons for a long period of time, but there isn't too much of a guarantee that the information recorded stays in-tact for long, unpowered bits of time.