Andrew,
Just had some to look at felt specs. I think a different spec would work better. The soft F-11/13 is made for impregnated uses, perhaps like an oil wipe. That may make it better absorb the fish glue. It's also available in 3/16".
http://www.thefeltcompany.com/...-16-thick-x-72-wide/
Why did you determine that you wanted the thicker material? Frank G. observed the original material, which was thinner.