Transporting source code securely

["Bill Stout" <bill.stout () greenborder com>]

Our developers occasionally debug at customers sites, and need to bring
about a Gig of proprietary source code with them.   

I'd like to secure the media they take with them in case they lose it.

I don't want to add software to the debugged machine in order to access
and decrypt the media they bring.  Both PGP and WinZip require software
to be loaded, although PGP acts like a disk, WinZip requires extraction
to use encrypted files (not usable).

I'm also skeptical of the portable biometric drives.  It appears that if
the drive were removed, it could be read in cleartext.

What is used out there to transport source code securely?

Bill Stout