[toast0]

I don't think they changed the plastic when they changed the shape, so I'd expect fuel vapor to permeate the old plastic cans too (or at least some of them). A metal can with a good seal doesn't let vapor out, so be careful with big temperature changes.

[porknubbins]

Ah that makes sense. I can definitely see the pressure buildup in the plastic type. If there is a risk of exploding metal jerry cans that would be quite a hazard.