Would you need regulated power when running off a dual battery? (I like cold beer too so I have one as well!) I would have thought the isolator would have kept all of the spikes etc at bay and a power brick would then provide sufficient regulation.
I run mine of a 12 volt brick power supply and have built a yet to be tested startup/shut down controller with a couple of relays. I was going to use Aux battery to power the Laptop but wire the relays to the igniton for startup/shutdown. I hacked the power switch and wired it to the modem port. The relays pulse when power is turned on and off and this closes the contacts on the laptop power switch to force a startup and shut down. The shut down is not really important as I can control that using power settings anyway. I will include an override switch to prevent shut down when the ignition is turned off.
I had not thought about regulated power for the screen either. Maybe I should!