Wrong or right, I went ahead and filled the scar on the side of my boat, and at least for now it looks really good. In fact, one would be hard pressed to even notice that the hull has ever been repaired. The following photo shows the primed repair work (the blotchiness in the photo is the primer - the finish is very smooth and fair). If the wind quits blowing today I'd like to get the hull and trailer painted in Duralux Duck Boat Drap.
After speaking to a buddy who retired from the auto body repair business, and reading other success stories for boat repairs, I ended up using Bondo Glass. It's nothing like the regular pink Bondo and according to what I've read, it's commonly used to fair the tunnels of jet jon boats (when marrying the fiberglass bottom of a jet ski to a jon boat hull).
This stuff was STICKY and the color/consistency of green slime immediately after mixing. It set quickly, and as each batch neared the end of it's pot life, you could see the glass fibers in it. It also dried hard, but not brittle. If I were to use this product again (or rather next time I use it), I'll practice a bit more economy in its application. I put too much product on the hull, and added an extra hour of sanding and fairing work to my schedule. A course 36 grit sandpaper on a longer sanding block was the ticket for the rough sanding, with it finished using 150 grit paper on an orbital sander. The finish is't perfect, but it looks at least as good if not better than the rest of the hull! The repair is now invisible!
I was fastidious with prepping my hull for the filler (wire brushing, sanding and cleaning with xylene), the repair is above the waterline, and this part of the hull has no flex due to its proximity to a bulkhead. The optimal way to repair this scar would have been to have new aluminum welded in, but given the value of the boat and what I'm willing to spend on it, the $15 can of filler fit my budget perfectly. Hopefully the prep work will help extend the life of the repair.
It'll be interesting to see if this repair lasts, or if it fails prematurely. I'll report back after the boat has been put through the paces. If my repair fails, I'm only out $15 and a extra hours of cleanup with a torch and wire wheel.
Cheers,
Scott