Always hard to say for sure but doubling or tripling your battery bank capacity will of course increase your time in batteries. Two battery setup is not much capacity. Most folks, I think you will find, need to run Genny a couple times a day for a couple three hours to charge. Typically in the morning to replenish batteries from the night and while prepping breakfast (microwave, coffee maker, etc.). And again in the evening when prepping dinner and to top off batteries for evening usage.
Vince and Susan
2011 Tiffin Phaeton 40QTH (Cummins ISC/Freightliner)
Flat towing a modified 2005 Jeep (Rubicon Wrangler)
Previously a 2002 Fleetwood Pace Arrow 37A and a 1995 Safari Trek 2830.