I have not used additives for my generator. Seems this would go into your vehicle fuel tank unless your model has a separate. You need to run your generator monthly for 1 to 2 hours minimum with a load on it! Run your generator when traveling into a Rest Area if necessary or when entering your campground. Operate the generator with a/c running for a load. Don't let it sit for months without running. Very Important!!
On my Forester #3051S, I had fantastic fans installed in all ceiling vents and even changed out the small fan in the bathroom. A strong fan in the bathroom/shower area is necessary for good circulation.
My Class "A" had fantastic fans with wall controls and they are really nice. The ones I purchased for my Class "C" did not have wall controls. But they are easy to operate, just open the vent manually and they turn on. You can preset the fan speed between 1-3 and it also has an IN & OUT switch. The fan will pull fresh air in or pull inside air out. My favorite is pulling air out and opening the windows for ventilation.
Your salesman's or dealer should help you out with basic supplies required. But, they can also have you purchasing stuff you don't really need. Just some basics are: toilet tank chemicals, sewer hose, sewer hose 90 degree elbow with donut and threads, clear elbow, Fresh water hose (white in color), pressure reducing regulator for water hose, electrical supplies: 30amp to 15amp adapter, 50amp to 30amp adapter, 25 ft 30 amp extension cord. I also like to have tire/wheel covers and some type of windshield cover. Some RV's have inside curtains or blinds already installed for the cab area. BTW..covering the windshield from the outside will reduce heat inside.
Standard Fan-Tastic Ceiling Fan Vent without Thermostat - Fan-Tastic Vent CW4000R - Fans - Camping World