Colin,
Please contact Steve Rander directly. Steve founded and operated Schooner Creek Boat Works (Custom built yachts and repair facility) for almost 40 years. He is an incredible craftsman. He also is an accomplished ocean sailboat racer. In addition, he has been a glider pilot for decades. Anything regarding sailing I'd listen to what he has to say.
Craig


Many thanks to those of you who sent in replies.
My plan is to look into the possibilities of making a set
of covers myself from Sailcloth. A few more ideas on
spec/design of Sailcloth covers would be appreciated.
Per Carlin`s contribution is great.