Rigging a pencil case So I have this pencil case:

And I would like to open it like this:

Note : I'm not trying to open the zipper, just to deform the pencil case in a realistic way.
I figured the best way to do this would be by rigging it, but the thing is, I don't know much about rigging. I tried this :

But, as you might have noticed, I kind of have no idea what I'm doing and it really does not work.
So, would you have an idea of how to get a realistic opened pencil case, with or without rigging ?
That would really help me !
Maybe you should try to rig with the Stretch To constraint, I give here an explanation for an arm (method #2), it's exactly the same for your pen case, except you'll need several bones all around the object. Also you may want more than 2 segments if the deformation is more complicated:

You may also want to try Spline IK but it's a bit tedious, so if Stretch To works fine, then use it.