Hi John,
I agree with Adam's suggestion that you consider avoiding an inverter for the laptop. They work well, but tend to guzzle the juice.
I have a current model Dell laptop which I power remotely using a DC-DC converter from JayCar (DC 120-003, 12v to 18-20v). The only time consuming part was finding a power cable/plug to suit the DC input socket on the laptop. I eventually located and purchased a suitable cable/plug (PL7450) at
www.laptopjacks.com.