I liveaboard in SW FL and I use an off the shelf Compaq Presario 1245 that is a couple of years old now. And I have a deskjet 712C that is about the same age. I don''t really see any reason for buying a marinized laptop.
Haven''t had any problems with mine thus far, but then its not topside when we are out sailing or motoring. I do it the old fashioned way...with GPS and Loran and keep track of my position on my charts.
By the way...it will more than likely be less expensive to purchase a 300W inverter to power the laptop and the printer. The price of a 12VDC cigarette lighter adapter will be more expensive...at least it was for me.