Just spend $8 to finish a sea sock. The fabric is nylon coated with one side vinyl. Only $3.99 per yard in Walmart. The advantage is that it is waterproof and one side is vinyl and can by sealed by HH-66. I just use the leftover fabric with HH-66 as seam tape.
Firstly, form the shape as a box, fold both ends like those of paper shopping bag. Then cut a hole on the top according to the size of the coaming, and finish the coaming area just like Tom Yost's removable coaming. http://yostwerks.com/SonnetCoamingSkinA.html
