Gelling and fuel treatment are secondary considerations - you need to run that generator at least a couple of hours under load each month! Onan recommends this action. A generator that sits will absorb moisture in the windings, which will negatively impact output and possibly prevent any output! Moisture in the windings degrades the insulation, and the generator output. It is non-reversible, and will require a generator rebuild or replace.
Jay & Jo Couture Livin' On The Edge,
w/Dawson, our mini aussie, in a 2007 Monaco Knight 40DFT, towing a 24" Pace garage.