You can glue in a servo, or fit it into the wing with style.

I've ordered a large flying wing made of EPP foam. To move the long ailerons, I chose this servo for its higher torque than your garden variety 9g servo. Yet it's smaller than a standard servo. This one is digital with metal gears, fairly fast and durable.

I plan to cut a slightly undersized rectangle in the wing and glue this mount in with clear Gorilla glue. It cures strong and flexible and can be applied thinner than hot glue, so probably lighter. It won't fall apart in a summer heat wave like hot glue.

Tiny screws hold the cover on. Or you could glue the cover on, or leave the cover off and secure the mount with packing tape.

The cover hangs over the edge of the mount to hide the mount/foam joint.

For the rudder I'll design a mount for a 9g servo, since rudder is only used on the ground for this wing. That will use the ubiquitous MG90S servo which you can find at 6/$12.50.

NOTE
Thingiverse is eating my updated body and cover STL files. They are in the file list, but they don't show up in thumbnails. Maybe servers are not processing STLs for a while to reduce the load. I'll try again later...