Be sure that turbulence will not loosen the tie downs. Once there is some movement, jerking will stretch it more. No way will I carry a full jerrycan. I have carried an empty can, well secured, at low level. A full can will exert far more newtons in turbulence. In rough water, I've watched things loosen tie downs on a boat, where I could tighten them. A loose full jerrycan could wreck a light aircraft.