After a frustrating start, I re-leveled the bed, increased the bed temperature, and printed a perfect guitar body.  It only took 49 hours, and essentially all of a kg of filament. As you look at the pictures, you can see the chambers on each side of the guitar.  As the print progresses, the chambers are closed up with an arched “ceiling”.  The cross-section shows how that was designed (to eliminate the need for support during the print).  If someone needs space for electronics, they can drill into the chambers from the front (to mount controls) and cut out an access panel from the back.