https://www.akustikstoff.com/Speaker-Cloth-Samples:::116.html
I am going to build my own housing for the unit. I came across this site that provides samples of acoustic cloth including waterproof at a reasonable price. It also is easy to treat the ordinary cloth with a water repellant spray.
Hope this helps.
Been looking into how I could do this -I think paypal and to cover costs would be (for UK) £1.20 for one sheet inc 1st class P&P and 30p per additional sheet, of course, if you are close to Bristol UK you could pop in. The sheets have filing holes and laser cut numbers so the max size of virgin sheet is 12x12 cm. My email is david at brownfamilymail.co.uk so you can drop me your address and I can send you a paypal invoice.