Carman works great for viewing the data.

Quick description of my setup (similar to most folks I'f guess). I have a Nokia N800 which I use in car for satnav (Wayfinder), Media Playback (Canola2), and Engine Data (Carman).
As I don't have a aux-in on my stereo I use a Griffin Itrip universal+ FM transmitter which has a usb port for connecting chargers etc. However I don't find that it supplies quite enough power to charge the N800 well. My friend, who also has a N800, has the Nokia FM transmitter which has a retractable lead and a built in flylead for power, which works really well - much better than the Itrip. I also use a bluetooth GPS receiver, and bluetooth to my phone which has a data connection. I use the keys on the frontpanel to swap between the 3 applications as needed and find that as a removable carcomputer it works great.

A few points on the initial post - If you are intending to mount the 810 in such a way that the hardware keys are hidden - why not buy an 800, which has a lot more storage capacity (i have 32GB), and is a lot cheaper. Also you could purchase a separate GPS receiver and mount that somewhere that will get the best possible signal and then connect to it via bluetooth. I also would suggest that in my experience you need access to at least the D-pad and home,menu and back buttons. The N8x0 is not entirely touch driven yet, although for media playback Canola is.

Also the charge for the N8x0 is 5v so you will need a converter. I would suggest obtaining a multi accessory socket unit, hide it, and either hardwire that to the car supply (fused of course), or just plug that into the car's accessory socket. Then use std in-in car mobile chargers for the tablet, and phone if required.

Gary