Tomterrific wrote:... After drilling the holes I took some leftover polyurethane and used Q-tips to seal the dry wood inside the holes....
* I use a similar method: drilling a hole, then liberally coating the bolt/screw threads with Loctite PL (or Gorilla Glue Clear Grip Contact Adhesive, if there is no washer to cover the spread of excess adhesive) before insertion. Then, I use stainless fender washers on both sides to make a waterproof patch, sealing the hole, before tightening the fastener. I wipe away the excess, usually.
* So far, with dozens (literally) of holes thru my 3/4" plywood structure, there have been no leaks, with most of the larger openings sealed 7+ years ago. They are periodically tested by thunderstorms every time I camp, so I am constantly observing their status, though I have great confidence that they're sealed for good.