This is a gentle trainer plane, so no huge stress forces involved i.e such in a high speed or large aerobatic plane.

I would cut a piece of ply the width of the inside fuse and 15 - 20 mm wide (high) and epoxy it in place (if you have the space) on the fuel tank side. Fill the original hole with a piece of wood & epoxy and redrill it later. Or, if you can still change the dowell in the wing, go for a larger diam dowel (get it from a hardware store) and drill out the skew holes to the size of the new, larger dowel - probably the easiest option.

The idea of the new piece of ply i.e 3 - 4 mm is that it now carries the load whilst the original holes guide it and help to carry load. Expoxy, especiall 24 hr type set rock hard. Good enough to fill hole.
Bundu