I carry a full 6 gallon extended run tank, plus three 2.5 gallon and one 2.0 gallon cans of gasoline in the rear of my pickup which has a Leer cap on it. They all fit snugly in one of those black heavy plastic cement mixing pans sold at Lowe's or Home Depot. I like the 2.5 gallon cans because they are easier for me to handle than 5 gallon cans.
I've never had them "contaminate" anything.
I need that gas to run the two Honda 2k gennys that I also carry. I need them to run the AC at home football games in the fall in September. It can get very, very hot the first couple of games. And when the AC isn't needed the extended run tank fuels just one of the generators.