All,
First, thanks for the detailed advice. This little repair was straightforward and is MUCH better than before. A few lessons learned:
Buy the Aluminum from Spruce. Their standard sheets are enough for a couple of "redo-s" and were cheaper than local suppliers.
The rubber gasket suggested in this thread was great, cheap and easy. Recommended.
Use the cardboard box that the Aluminum comes in to make your template. A "thin" roll of blue painters tape and a sharpie works great for tracing the contours of your empennage after your get the first cut done.
I used air shears. I can't imagine using anything else to cut the metal.
