Rings - Well ya, on the right END side of the door.
One would be enough, due to the ribbing on the door keeping it rigid in one direction,. centred on right side end
Northerner's barrel bolt does nothing to "pull", only align the in to out direction.
But, the door is floppy in the other direction.
So that's why he needs something to align it in center.
Accomplished by bending door radius tighter than the can body, then somehow pressing in top and bottom center to smaller radius to minimize gap.
THEN, after that, his barrell bolt will be OK.
It is probably loose enough to very easily slide to the correct depth.
Am I talking too much? Marc