What will protect the key from being mounted and read by testdisk much less brute force attacks?
The key isn't hidden. It can be cracked.
Of course it can be cracked. your previous post suggests that it wouldn't take about a week running on a Cray to crack AES encryption.
Supercomputers Don't run FreeBSD. Obviously you've been told otherwise. Also, I doubt you have a supercomputer.
Also, I'd imagine that somebody would notice their encrypted drive missing for a week. Of course, with a "typical" 2.33Ghz Quad core, it might be a few months.