Mainlysteam would have made a much better job of that - Henry Claymore - our neutered Tom spends much of his time licking where his nuts once were - do you do the same?
I've got an old Toshiba Satellite Pro (think its similar to yours).. do'nt bother with the inverter and just wire it straight to the boats 12V supply and it works fine .. the laptop battery , I beleive, smooths out power fluctuations.
This is pure conjecture as I haven't done it, but I think you could do a setup like this:
1x "hard as nails" Laptop, with a decent graphics chip that supports running an external monitor
1x Ultra tough keyboard and trackball ( as seen in BT Internet Phones), they cost about £150 if I remember correctly.
2x "Hard as nails" tft screens, one mounted in front of the chart table, the other in the cockpit (you can get little 10" ones for about £100, I'm sure there must be waterproof versions as well)
If the laptop graphics chip doesn't support 2 monitor outputs then you're stuck with the monitors being the same size and buying a £50 repeater, or ditching the keyboard and keeping the laptop on the chartable instead of hidden away in it.
If you were really cool then you might have a touch screen waterproof joby in the cockpit, but they easily cost 2x as much