1.  Ensure that CLOSE_SESSIONS is set to yes in /etc/login.defs, otherwise
your volume will not be unmounted upon logging out.

2.  I had no luck when using the Debian mount binary to mount an encrypted
loopback filesystem using the keybits option.  I had to build my own
mount binary using the patch at kerneli.org.

Bug reports have been submitted to the Debian project documenting
these issues.
