As with most things there is always more than one solution. The solution that I currently use is a cheap 2 stroke genny (ebay £40) and one of these:
http://www.amazon.co.uk/APC-Line-R-1.../dp/B0000C88CR
I was lucky to get one of the bay for £25
This stabilises the genny output to somthing more reasonable and in the 3 years I've been using this set-up I've had no failures of PSU's/chargers or laptops.
The down side is its heavy and takes up more room in the car. The regulator gets warm and reduces efficiency of the whole system. But it was a cheap solution for me at the time. Yes a nice inverter genny would be preferable but on a budget this worked for me.
Matt