Timmy
My suggestion would be to build the wing, then make a motor pod with an underside that exactly fitted the top surface of the wing and simply glue it on. The motor pod would also sort of act a partial dihedral brace.
I did thus on my scratch built 'push pull' which has a very similar layout to yours but has two motors in tandem.
View attachment 178400
You can see the spar running through the motor pod.
Of course it makes it a 'one piece' plane (nothing is removable) but it is light and strong. It was built in
2012 and it is still going strong.