Personally, I don't put anything in the tank. My Crossfire will be driven most of the winter, and on my 1967 El Camino we have never used anything and have had no problems. It has original tank, and Engine and Carb were installed in 1997. Carb was cleaned out once after about 13 years of use. Fuel nowadays is much cleaner and has so many additives, I don't think it is as important as it used to. I do try to keep the tank as full as possible, to eliminate as much of condensation as possible on the bare steel.