I currently do not charge for generator rental. My rational is that the amenities of the trailer are not fully operational with out it. Charging for it is like rental car company charging extras for a/c or a heater. I include the generator for free with 2.5 gallons of gas. This included unlimited hours but they have to provide their own gas outside of the 2.5 gallons included. I have yet to have someone go through the 2.5 gallons though. I think you are better off charging a fair rate for the trailer that include the generator then making it an add on. It already feels like a bunch of add on's with cleaning fees, insurance, taxes, and Outdoorsy fees. Too many add-ons for basic things can end in sticker shock when the renter see the final price. Just my two cents.