You could use a 2GB SD card with a USB adapter for this because its cheap and has the added advantage of a write protect switch.
There is no reason I can think of that one SD card can't be used with multiple wallet.dat files and you should be able to copy one SD card to another for backup purposes.
SD cards are
not a secure floppy replacement: They include CPRM with device revocation. The "Secure" in "Secure digital" means "Secure from the user," not "Securely holds your data."
I
Have already said in my first post, computers are too insecure to handle a crypto-currency in the near term.
Yes, the write protection switch may help you avoid accidentally deleting your keys. Also blocking some virus from getting onto the SD card. A write protected USB is hardware protected, but harder to find.