I had two of those style cans. Mine had a spring loaded flap to seal the when the funnel was folded over. I made a cage for them in the boot. Took the wife shopping one day and left her putting shopping away while I went off to get something-or-other from another shop. On the way home after, I got the occasional whiff of petrol but put it down to other's exhaust fumes. Arriving home I opened the boot to discover the two cans on the boot floor empty because the wife had moved them to put eggs in the cage to keep them safe. The only things we salvaged were the cans and bottles. Threw away all the fresh fruit and veg and the bread, cakes and rolls. Couldn't put any fresh stuff in the boot for months after because it took that long for the smell to go.
With the one I had, the spout/handle folded over compressing the seal on the can, went under a retaining piece and was locked in with a retaining pin.
It was steel, very strong, I think it was made by Remco?
It was advertised as fitting under the drivers seat - how times have changed!