I would recommend using stainless screws for attaching track to the gunnel of your kayak.
The plastic is very thick in this area, and you can get away with using sheet metal screws for light/medium duty applications. For heavier applications, I'd recommend thru-bolting and using a small washer and nylock nut to back it.
Suggested fasteners:
-1” track requires (4) x 8032121 screws
-4” track requires (8) x 8032121 screws
-8” track requires (12) x 8032121 screws
80048021
TRACK, 1" LOW PROFILE SCOTTY
80048022
TRACK, 4" LOW PROFILE SCOTTY
80048023
TRACK, 8" LOW PROFILE SCOTTy