Welcome, Ed! Nice to see you over here.
Did you ever find a good source for the plastic hulls? I have a buddy who is former LEO and he said the only local/state LE agency in VA that would have them would be the state police, and they have no local office that interacts with the bomb disposal unit. I think I'll be stuck with the converted .50 BMG cases no matter what.
However, I've been so busy with other projects that I can't even consider building one of these until I get some things cleared off the table. This is probably a "next year" project, maybe a 2010 project for me!