I saw a really neat one recently.

The fuselage was a thick profile, perhaps 1 inch thick, but it was still a profile. The wing spar of one of the two wing halves was bound/glued/stuck to a carbon tube - again about 1 inch diameter, which passed through the fuselage (via a fibreglass tube) to the other wing half, which used a fibreglass tube to slip over the main carbon tube. A smaller diameter carbon rod was used at the rear of the wing halves through the fuselage.

The ensemble was secured using a single bolt, tapped into the main carbon tube. There were also small flanges on the rear of the fuselage to aid alignment.

Very nice constuction, simple and it flew very well.

Rudy I hope this works

Clever Brazilian electric profile.  One may not want to try this with an internal-combustion-engine-powered profile.