Nice design. I can see it was a challenge to work with.
For cracks in wood, as soon as I see them I treat them with CA glue, usually medium thick, and let it cure. It slows the process but saves worse problems like you had.
For Inside hollowing I have had good luck with Munro's hollowing tool. The way it works makes it almost impossible to get a "grab" or gouge so I have a lot more confidence working "blind" inside....but it is not cheap. Packard Woodworks is the only place that seems to carry it. It comes from Auatralia.