After trimming the bottom 1/16th inch ply to the bottom of the fuselage I applied a coat of varnish to the interior. I was a little surprised the bare wood soaked up a whole quart but it went on nicely. It did run through in a couple spots and I will have to sand a few places where I didn't think to put masking tape. As a side note: the T88 epoxy does not stick to polymer - what a surprise. I sent a question to the volksplane builder's forum and got a great response from Fritz Wagoner:
(ref: page 15) The gap between the bottom of the rudder and the top of the
1/4" ply plate is ~5/16". There's plenty of room for bolt heads, especially
if you use something like an AN525 machine screws. ...maybe put AN970
washers under the heads.
https://www.aircraftspruce.com/catalog/hapages/an525.phpYou could also cut a shallow grove (or two) around the OD of the bushing
that will fill with epoxy and mechanically hold the bushing in even though
the epoxy won't stick to the bushing.
Don't loose sleep over it though, the top bushing can't fall out. The
bellcrank sticking through the slot in the F-15 bulkhead keeps the rudder
from moving up and down.
HTH
Fritz