Sounds like you have put some effort in so take your time.
I would say don't put any non slip grit where you will put your butt. It will destroy your gear quick as. The photo shows where you might put some.. ie black strip. Noprene or similar is a good idea as it won't harm any kit. Try your product and contact adheasive on small board first.
I tried mine, put it in a sink of water overnight and when it wouldn't budge I knew that was it.
Sail fast.