Propane Usage 2500 Watt Onan

I have the 2500 Cummings (Onan) LP generator. Found myself in Georgia in a Walmart parking lot one particularly hot/humid evening. Started the generator and turned on AC. By the next morning (about 10 hours later) it had sucked most of a 30 lb tank (7 gal) dry and the generator died because the tanks was so cold that it had frosted up on the outside. Switched over to the other tank, finished breakfast and hit the road. Compared to a gasoline powered (Honda), not a great choice for efficiency or even quietness but it is handier than heck.

If I was really going to boon-dock for an extended period of time, I would load up my Honda EU2000.