You didn't say what size genny you have. I have a Cummins Onan 5500 watt the manual says it burns 1/2 gallon an hour with half load and 1 gallon an hour at full load. When I'm running both A/C units off it 1 gallon an hour looks about right on fuel usage.
Sorry to hear about you being broke down and like you said at least your in a gas station parking lot and not stuck on the side of the road in the middle of no where.
Hope they get you going quick let us know how it turns out. Good luck
2014 Palomino Columbus 3650TH
435AH 12V VMax Charge Tanks, 520 watt Monocrystilline Solar Array, Morningstar MPPT TS-60 CC,Morningstar Remote,Cotek True Sine Wave Inverter,Cotek Remote Controller,50amp Progressive Hardwire Surge Protector
2015 Dodge 3500 6.7L 4X4
2011 CanAm Commander XT 1000