For those of you not following my progress on TRF, and are yet actually interested enough, here are some updates:
1. We've switched to poly casings. They don't insulate as well as we'd like, but they have not breached. The heat leakage is doing a little damage to the rocket body, but we can handle it.
2. We're having nozzle problems: they keep blowing out, and causing unpredictable flight.
3. Using a band-aid "solution" to these clay failures, we used some poly glue to help support the clay, and had some surprising success. We got about a 350-400 foot flight before the front plug blew, and the whole rig crashed. On recovery, all that was left was an empty tube, though we're not sure when the nozzle failed.
4. We set up and successful used a recovery charge, although the main nozzle blew out and the rocket crashed early, so it was in this case useless. Still, it's good to know that our delay system works.

We have been using diatomaceous clay rather than the usual bentonite for our plugs. Diatomaceous is quite rough, so we had hoped it would work as well or better. We couldn't find pure bentonite, but we have gotten some slightly contaminated stuff to try. Also, following some advice from TRF. we will probably begin forming our nozzles better, rather than just using cylinders.