Nikos, I think the Hatori pipe is long enough that the mount should be just inside
the opening for the pipe tunnel. If it was me I would glue a small piece of plywood
on the inside of the tunnel for just a little support for the mount then you will have to
cut an opening for the pipe stinger on the belly of the airplane.

I used carbon fiber push rods with titanium ends so they can be cut to any length you
need them. I also cut openings and glued servo mounts inside the wings so the servos
could be mounted outside the wings like I've always done on my other airplanes. The
internal servos were just too much trouble to mount and dismount and this way I could
use my regular servo arms.
Oh, I almost forgot...those little plastic screws that hold the lower cowl on , throw those
away and replace them with metal ones , they will break after a couple of flights.

tommy s