This is a derivative from http://www.thingiverse.com/thing:213858. I just hollowed it out put in a thread and created a threaded plug and voila. It sits up a little higher with the plug in as can be seen in the last picture.
Ok, not complicated but I've only had my 3D Printer for a week at this point. My plans are to put one out as a micro geocache next Easter.
Printed in ABS with a .2 layer height, 10% infill. No support needed. Used a Sharpie to color in the eyes.
I've printed 3 so far and the threads fit from tight to 'very tight'. I didn't adjust because having them very tight will make it more water/weatherproof if I put it out in the elements. I've noticed that the threads screw together a little easier after screwing/unscrewing a few times.
Derived from: http://www.thingiverse.com/thing:213858