Hi Mark,
It also depends on how much slewing you do, but
I'd go with a 100Ah deep cycle Marine battery, and power everything you can off 12v.
Run the usb hub off a jacar dc to dc converter (
http://www.jaycar.com.au/productView.asp?ID=AA0218 )
If the laptop can be charged off 12v do so. Restrict using an inverter to the smallest necessary then use a pure sine wave.
I've modified a jacar dc-dc converter to supply more current for the 9v for the Canon EOS.
Monitor the battery voltage with a plug in voltmeter
http://www.jaycar.com.au/productView.asp?ID=QP2220
and start charging it via the car if it drops below 12.0v
Hope this helps