I agree; bind the soft skin and weight them then constrain the hard surfaces to the joints. If you want to bind the hard surfaces as well, you could paint their weights onto a single bone so that they will not deform when the joints around them rotate.

To make things easier on yourself, you could put the hard surfaces on a seperate layer than the soft surfaces so you can turn them off.


I like the rig you made!


edit::: Is the model one piece? I don't think so but if it is then you can still bind it using soft skin then paint the weights so that the hard surfaces are ONLY being influenced by a single bone and then make the rubber surfaces weighted between 2 or more bones so that it stretches when the joint bends.