i used 1 for years
i used to carry my cart and 10 barrels
i had a passet estate and a fiat marea weekender
i used to spread the weight about
the cart and 4 or 6 barrels in the boot
2 barrels in each foot space
1 day per 6 weeks, i used to have to carry more water, so i used to put them on the rear seat and seatbelt them in
i knew the risks about unsecured loads etc etc which is something to keep in mind, as if you have a accident and them 25 L barrels start flying around, it will not be pretty, but i knew the risk