2GB should be enough, i suspect that Persistance is not working in your setup, so instead of writing to USB everything is kept in RAM which gets it filled.

You can test it if you check that after reboot the files that you downloaded and supposed to written on USB are there after reboot.

Either way, i'll go through that procedure once again during weekend, as mbk will update boolbd fix in his repo and i bought USB 3.0, so i'll try it myself once again to see what might be the problem.