I use to run a old Dell latitude xpi in a large dock under my honda driver's seat. the key item was a small foam pad under the dock to help reduce some of the road bumps. I re-used some soft gray foam that I usually found at work to pack harddrives or PCI cards.
Also note that port replicators with PCI slots draw more power and usually require 90W or more to run....when a laptop power is usually 45w. found that one out the hard way.