Don't trust him.
It may just be me being a nosy sod but after a while I'd be itching to find out what is so important on those drives.
Seriously though, if you have data important enough for you to go to such effort to keep a copy safe, you may as well go the whole hog and keep it at your banks safety deposit.
Personally I would grab a couple of ammo boxes from an army surplus store. As long as the seal is still good and there aren't any holes, it will be air/water/fire proof, so in the unfortunate event of your house burning down your backup will be safe.
Either an external enclosure or a caddy system would be a good idea so you don't have to open up your pc every time.
fwiw I currently have no backup regime even though I know I probably should. Pure laziness.