This is a large bolt with a hidden compartment. Included is room for a sealing washer (which can be printed in a flexible filament) or o-ring to seal the chamber.
The compartment is 0.8 inches in diameter and a little more than 3.5 inches deep. Plenty of room for a few log sheets and small pencil.
The thread is a 1 1/2-6 UNC for the bolt and the internal thread is a 1 3/8-6 UNC.
Sliced in Cura:
0.2 mm layer height
1.2 mm skin
1.0 mm top/bottom
Print the bolt head and shank. Place a seal in the bottom of the bolt head. Screw the pieces together and bottom. You may need to work the threads a little to loosen them up.
I printed this in Black ABS. After assembly, I sprayed it with a couple coats of spray acrylic.
I printed the seal in ninjaflex, but wasn't happy with the result so I just used an o-ring.