Looks great Greg

I used to hollow things out the old school way - marking out and carving out with a scalpal and carving blades, and finishing out with various files and sandpaper. This is very satisfying, but also time consuming. Easier now with modern tools like the Dremel and even newer chordless mini drills (amazing things!) with a grinding bit, then finishing out with files and sanding sticks, sandpaper etc.
However you did it, looks like you nailed it anyway.