I thought about a few different approaches but settled on this:

Made some 1/4" ply from 1/8" ply by laminating (one side at 90 deg) with gorilla glue and clamps.
Glued a 1/4" ply strip under the existing rail (it did not go all the back to the next former).
Glued in a stub 1/4" piece on top.
Glued a 1/8" ply on the side over the joint for strength in the vertical.

I put the blind nuts only on the stub piece and cut the bolts so they only went that far. That way, there was full strength on the bottom rail.

Some photos on the steps...

In the same "landing" the wing tore off the fuse too. I was surprised the nylon bolts did not break but instead the mounting plate tore out (I had epoxied that too). There is not a lot of strength on the fuse sides where the wing bolt plate mounts. Anyway, that just glued right back in. A bit of covering on the wing to fix too.

Back in the saddle.

(PS I have only had this one out twice and both times parts came back in the bag and I spent the next few days fixing...not to mention the ribbing from the wife and kids about "crashes".)