[VHFcontesting] Inverters for rovers

[k4gun at comcast.net]

I'm now in the market for an inverter for my rover station.  I need to power a laptop and the rotator for the antennas.  The inverter will be mounted next to the aux battery, inside a steel tool box in the bed of the truck.  It is my hope that the steel box will make for a decent Faraday cage.  

My question is what kind of inverter do I need?  Can I get by with one of the cheap 300 watt models?  Do I need a "pure sine wave" model or would one of the modified wave models work?  I'd appreciate any suggestions here.

Steve