the area of cored laminate involved is the area of the annulus you decore and replace with epoxy. I do a pretty good job there, and so it is about as big as a fender washer for that size bolt. Using a 1/2 OD insert for a 5/16-18, I would decore at least 1/2" back. Now I have a 1.5" diameter donut of hardened laminate. I would not use this method to mount the anchor rode cleats, but it is pretty good for a lot of stuff. A large backing plate usually going to be stronger, but I personally guarantee that those ice chests will be in shreds before the method I described is damaged in any way!