I was thinking that the mast bearings would work quite well for the rudder shims. I bought the $6 kit from hobie and the shims they supplied were about a 1/32 of an inch thick. Didn't really do much for my 20 year old castings. The mast bearings are about a 1/16 of an inch thick and probably would work pretty well. But I will say that the milk jug idea sounds whole lot cheaper.