The metal pots had a screw top lid and (if I remember correctly?) a soft seal - so they were in fact air and water tight. The plastic ones are neither, but still pretty dust-resistant. Getting a few grains of dust or sand stuck in the felt light-trap is unlikely to be good news, so some sort of protection is a good idea.

Multipacks of Ilford 135 film are/were indeed plastic-wrapped like the 120 rolls. Probably the most robust combination is those 120 rolls which are in the heat-sealed plastic and then put inside a big plastic pot, as that gives both gas and dust protection. EDIT: - I just checked my stash, and I have mis-remembered this as the rolls sold in the pots are not inside the plastic stuff after all, oops!