to make the elasticy skin you are asking about, use knox gelatin. Cheap stuff. But you'll have to fuck with it some to get it to the consistency you want. The best thing to do is just experiment.

If you want to see a behind the scenes look at some great looking limbs, skin, etc., I'd recommend the 'Flower of Flesh and Blood/ Making of Guinea Pig' DVD. Yes, it's in Japanese and you'll have to use your imagination (since some of the subtitles don't translate perfectly), but some fantastic gory fx on there.
CK