Galvanizing is actually a Zinc coating done either in a hot plating tank or done in a cold process. I dont think your paint would survive the hot process.
Both might require a sandblasting or metal etch done with acid to make the zinc bond with the steel of the tank.
I'd look at either the Kreem sealant kit for gas tanks sold at the bike shops or another one called Por-15 that can be found at
www.por15.com
