Using a 240V inverter is less efficient than straight DC-DC conversion, plus there's the extra safety concerns - especially since a lot of the cheaper equipment isn't rated for outdoor use in the dew.
Have a look at your laptop's power pack and see what the output voltage is (probably somewhere between 15-24V for most laptops, or less for netbooks). I think the laptop car supplies you're talking about are similar to
this one from Jaycar (what I use)? The 150W rating is the
maximum power consumption - if your laptop draws less, it'll use less.
Are you also going to be needing power for dew heaters, USB hubs (more reliable externally powered), cameras, mount etc? I run everything - mount, cameras, hub, Macbook, dew heaters, etc - off a single 110AH battery. During warmer months it can supply enough power for two consecutive nights, but in winter it'll start alarming low voltage half way through the second night.
Aussie Batteries & Solar currently have a
deal going for a 120AH battery, only $289. Several people on IIS (and that I know of off forum) have happily purchased from these guys - including myself. They also have a kit including the
120 AH battery, 120W solar panel, regulator, etc for $649.
By the way, 100+ AH batteries are *HEAVY* (30 kg+) and somewhat difficult to move because of their shape. If that is going to be a problem, you can buy multiple 40-60 AH batteries and run them in parallel.
You'll also want a charger that supplies around 10-30% capacity of the battery, i.e. a 120 AH battery should have between a 12A to 36A smart charger (3 or more stages). If you'll be charging it via a generator in the future, you'll probably want one towards the higher end so it doesn't take too long.