I would not advise using shrink sleeve on chain - it makes the chain into a stiff rod because the links can't move. Shrink sleeve once shrunk is much stiffer than the original unshrunk version and is not intended to be very flexible. When I tried placing chain inside a normal plastic tube for a bike lock it just held the water in place so even the galvanised chain started to corrode within a short time (guess it would be OK with stainless chain but that's expensive). If the chain can't move freely it might also start to have a small negative effect on the holding power as the links are always held together so do not move with the rise and fall of the boat in the same way.
Mike C - Tarka 26M