While working in the shop with the kids today, I put the welding rods back in their screwtop plastic case (water proof) of course, and made it back to the classroom and then it hit me. For a backpack PSK this might work great. You could even use it for water if you had a way of carrying your other items.

How heavy is it?

They are not really heavy (unless you fill them with rods - then they get heavy)

That's one heck of an idea!!

Next time I'm out buying more rods...

Not any more than a piece of 2-1/2" PVC pipe and 2 caps. The one show lists for about $7.

If not overlypacked with dense items some styrofoam could be placed in the top, and bottom, and it should float as well.