I pulled factory generator and the compartment would fit 1 -5 gal and 1-2.5 easy.
Was even thinking about lowering compartment floor for fitting more cans, but with Honda efficiency that never was needed even in 115F weather.
For colder day - filling up generator tank was all needed as that would last for 4-5 days of using coffeemaker, microwave and charging.
If you don't have that option - I would not hesitate to stand 5 gal can on the bumper and rope it to the ladder.
That might by questionable by the law, but what isn't ?