Random Fuel Hauling Question

So this weekend I’m hauling a trailer down to the coast. Subaru outback, 3.6r touring. Pull a utility trailer, a 17ft boat, all no problem. I also have a roof rack and a hitch cargo rack.

I’m going to be knocking some project out on my boat this weekend including pulling some old gas out of the tank. I’m leaving the trailer down on the coast and coming back to the city. Coastal small towns only have hazardous waste disposal about twice a year- city offers it all the time. So I was thinking of bringing 10-15 gallons of old bad fuel back with me, sans trailer.

Don’t like the idea of having the cans in the car. So, turning to folks thoughts here: would you put the gas cans on the roof rack or on the hitch rack. Would exhaust be a concern on a hitch rack?

Trying to minimize my rolling Molotov cocktail potential to the best of my ability, but probably overthinking this.