I checked into the same thing. I looked into a 10,800 watt generator. The salesman told me that in would require a 150 gallon propane tank at 60 degree ambient temperature to suffice the pressure needed by the generator. Now on the back of my food truck I planned on only having 1- 100 lb propane tank. 1- 100lb propane tank only holds about 24 gallons of propane. So even if I put 2- 100 lb propane tanks I wouldnt be able to suffice the gallons required by the generator. This generator also used 2.2 gallons of propane/hr. So in a 5 hr shift the generator alone would use 11 gallons of propane at about $2.40/gallon= $26.40. A good gas generator will use 1.125 gal of gas/hr. So with some math= 5hr*1.125= 5.625 gallons of gas in the same 5 hr shift. Here gas is about 3.46/gal *5.625gal= $19.46. So it would cost about $7.00 more per 5 hr shift. 5 days a week, 30 weeks a year== $1050 more in fuel cost per season. These numbers are in my area and how often I will run my food truck. Now you still have to suffice the gallon requirement. You need 150 gallons at 60 degrees, which means about 6-100 lb tanks! Just for the generator! I still have my cooking equipment to run. The colder it gets the more you need. At 30 degrees I would have needed 250 gallons.
Now this is the research I did based on my needs. All of this was a little out of my element. And I hope I researched it appropriately and I didnt just blow a bunch of smoke up you know where. Hopefully someone with more expertise in this will confirm what I have said.