Looking at the Onan specs on-line, consumption for a carbureted 7.0 gen set are .4 gallon per hour at no load, .7 gps at half load and 1.2 gps at full load, per their document a-1426.phf. Yours could be different depending on which gen set you have.
If in the large bag of documents Tiffin supplied with your new coach you did not get an owners manual for your specific gen set I would highly recommend going on line to Onans website and downloading the appropriate manual, it has a wealth of information that could prove helpful.
Bruce
