From Wes Giles “Spring Fever” C387 #53:

Haven’t seen this topic on this list yet. Last weekend while on a mooring at Ithmus Cove Catalina Island in a fairly heavy and steady rain; very unusual for So California, water started seeping through the canvas. Spring Fever is a 2004 387 with original canvas installed by a local (Marina Del Rey, CA) canvas provider. The boat has always been kept in-slip, so it is exposed to the elements (both sun and rain) year round. Has anyone found a way to remedy such a situation before? I have to believe there is some compound that I can buy to apply to the dodger that will provide water repellent results.

From the Sunbrella site:

http://www.sunbrella.com/en_us/how/cleaning/marine-tops-covers.php

From Mike Moorehead “S/V RHYTHM” C387 #29 :

My canvas shop recommends 303 exclusively for Sunbrella. Avoid getting 303 on your Eisenglass or other window material. 303 spray