At the recient wood boat gathering in CT there were 4 skin boats - one of them mine and I know all the other builders. We all used polyester 10 oz. - George Dyson . Two of the kayaks were coated in tinted epoxy and two used Polyurathane varnish.
Bill Lowe (Willow kayaks) In MA was a great help to me in researching skins. He builds over 20 skins every year etc. He uses Poly,. with a 2 part urethane coating. thge polyurethane that my friend uses is regular varnish out of the can etc.
Two things. Nylon is very unstable. When it's wet and cold it's loose and nice when it's hot and dry. I paddled with a guy this weekend who made a skin in a class in Mystic- used Nylon w/polyureth and varn. His was all loose and puckered.

The polyurethane fabric has a 15% shrink with extreme heat (torch or industrial heat gun) It's very stable. The epoxy coating that my friend and I use (two years old) is bomb proof. And so far my friend with the polyurathane coatings has held up great.

All the canvas boats I encountered weigh a ton. Canvas is heavy, rots and takes a lot of paint to fill etc. And, it's not as durable as the polyester.

We used regular (RAKA) epoxy for coating with epoxy tints added. I believe we the first to do that and a lot of people , including Bill Lowe considered it not a good idea. It's worked out great. The kayak skin still has plenty of flex. I did a lot of test panels before I did it.