Here is a great tip I got from a friend on how to install cowl mounting blocks. As shown in the picture, you drill a hole in a piece of hardwood. Then insert and glue in a piece of Golden Ny-Rod ( you never use all of it for push rods). Now you can use servo mounting screws to install the cowl. The screws fit tightly into the Ny-Rod and will not back out (self-locking). They don't require blind nuts or loc-tite and will hold up to numerous insertion and removal of the screws. Besides which, they are cheap and easy to fabricate.

To prevent stress cracking of plastic and fiberglass cowls, you can also drill the holes in the cowl large enough to insert the rubber grommets used on the servos. Paint the outside of the grommet the same color as the cowl and it looks pretty good. Not exactly scale, but works well for most sports flyers.
I'd Rather Be Flyin'
Vic