Gak!  my dual-box bowed dulcimer thingy I built a long while back it collapsing!  The boxes are bolted together, but one of the boxes - the lower one - is splitting at the seams and the "soundbox" has started collapsing.

There was very little reinforcement inside as I recall, and it is glued shut, so it will take a bit of doing to open it up and see if I can reinforce it so it can be played again.

In dual-box builds like this since then, I"ve glued in corner supports and screwed the boxes shut - two helpful things that might prevent a future implosion.  And this one  has separate floating bridge, not a neck/fingerboard that runs along the whole instrument.

Here is a photo from when it was first finished.

Live and learn!