I'm no expert, but an eighth inch seems a little large. 1/16th sounds better.

I would just seal the hinge line with clear shipping tape or the covering that you used to cover the plane, that way the gap size doesn't matter (on a .40 sized trainer).

I've had both of those planes, the Eagle II and the Aerostar 40 and learned to fly on them.

The elevator servo failed a few months ago on the Aerostar after 9 years and over 1,000 flights! What a tough bird! Building another for my grandson to learn on.

Good luck and happy flying!