I cut a piece of pine 2x4 to the length of the inside of the box and ran some 3-inch drywall screws through the box side and into the ends of the board. I screwed the neck onto the board. Very sturdy, and actually put the balance point of the guitar at the strap button.
I did a couple with a Block down the middle like a semi hollow body. It would attach like Teds But has hollow chambers on both sides.
That is exactly what I did on mine.
If you do a quick search in the picture gallery you can see how other people are making theirs. There is a recent one that shows the inside, very similar how I did mine.