[warthog5]

I'll give you a little diffrent play on what Roger said.
You can buy large suringes from the drug store. They run $1 to $2 for a 60cc suringe. If you wipe them out with a paper towel and shoot actone thru them twice you can reuse them time and time again.
Use an old tooth brush to wet the core out in the hole first with stright mixed epoxy.
You can cover the hole when filled with just Duct tape. No need for waxed paper. the area around the hole must be dry for it to stick. Duct tape will not stick on wet epoxy surface.
Before you start to fill the holes. tape right around the holes and put a piece of Visqueen all around it. That way any spillage is a easy clean up with just removing the tape and visqueen.
I recently installed a kicker motor bracket. I used some stainless steel tubing and stood it on end. Filled the tubing full of epoxy/cabisol. then I beded the tubing in the holes with more epoxy/cabisol. The new mounting holes were drilled thru the middle of the stainless tubing. 4 holes with 5/16 carrage bolts to hold the unit on. I garantee you could pick the ass end of the boat up off of that mount. It had alum backing plates on it too.