Oldgold - I don't have an exact number since it runs off my fuel station tank, but based on the gauge I'd say it took about 6 gallons to run it for 12/14 hours a day.
I took an external generator too, and ran the A/C on that during the night to 1) give the Onan a break and 2) so I didn't have to listen to the Onan which is right below my bed. That one ran for about 10 hours at a time on a 4 gallon tank.
Just me, my girlfriend and our crazy Boxer Stella.
'13 GMC 1500 Sierra Denali, '14 Stealth SS1913, '08 YFZ450 with some crazy engine mods.