This picture shows a smaller "fillet" under the stabilizer. Apparently, I used square stock for this, which has worked out fine.
One other thing I might mention: since our field is asphalt, I put landing gear on this plane so we could take off and land, hopefully in one piece. You can see the tailskid in the picture. For the main gear, I cut a piece of 1/16" plywood to the outline of the firewall, then cut a square notch in it from the bottom. When the engine is screwed down, this creates a pocket which the wire landing gear can plug into. It works fine, but I have come up with an improvement, should I build another in the future. That is, make the pocket narrower at the bottom and make the "loop" in the wire gear tapered to match so it will hold itself in better.
For training flights, I use a huge fender washer for tip weight, and fly on .008" x 42' lines. It keeps the rotation rate down, and the line tension is good, even in a decent breeze.