I also like the idea of using a laptop in my vehicle as my main GPS. Anyone interested in doing this may want to take a look at Ram Mounts as a way to mount your laptop right next to you.
Not the same company as the Ram truck company !
These folks have been making a large variety of heavy duty ball and socket mounts for a long time - marine, motorcycle, aviation, bicycles, cars/trucks, etc. I have used their mounts in boats and trucks and they are very, very good products.
I believe their laptop mounts attach to the passenger seat mounting bolts.
Tim (no connection to the company, but I do like their stuff)