If you do go with a toughbook I would like to offer a few recommendations:
CF-27 300mhz, very durable and cheap at twice the price. Make sure it comes with the hard drive caddy and a battery with at least half a hour life to act as a UPS.
A CD drive is usefull but doubles the price. Debian (amongst others) will do a LAN install booting from a floppy with no problem.
Distro. I have run debian and ubuntu with no issues. Slackware reportedly has no issues. Not sure about others. If there is any trouble inserting and ejecting pcmcia it needs a kernel command added to menu.1st, cant remember what but can look it up no prob if needed.
12v charger (duh
The shock protection on the hard drive is second to none, same for vibration. However it would be worth using a pcmcia to compact flash addapter and backing up to the solid state medium especially if using the hard drive that came with the unit.
Mind the rocks.