Sorry; forgot to answer this!
At joints, we had a parachute bay in the middle of the bottom section. The parachute bay is exactly sized to hold the main - this is important! Sitting on top of that is a spring-loaded man-rated pilot chute for a reserve. You can buy them on eBay for cheap. That tube (we always used LOC 7.5" tubing) sits in the middle of the lower section. The upper section just has a flat 3/4" plywood bulkhead on the bottom of it. The two sections are joined together buy a half dozen 1/2" nylon bolts. The sections are brought together with the spring-loaded chute sandwiched in at the top of the parachute bay. There's a rod sticking out that holds the spring in its compressed state. We put the two sections together with that rod in, then put in the nylon bolts. Once they're partially tightened, we pull the rod out, releasing the spring. Then the bolts are tightened the rest of the way.
Those nylon bolts are drilled out (use a drill press, not a boring bar on a lathe), filled with BP and two electric matches, then plugged with epoxy. Each match is wired to a firing board that is wired to an altimeter.
When the rocket hits apogee, the alitmeters trigger the firing boards, which then dump an R/C battery pack into the matches. The bolts shatter, allowing the two pieces of airframe to separate. The spring is helping push them apart and once they do, the pilot chute pops up and out and pulls out the bagged main.
This method has worked very well for us and it's stupid simple.
-Kevin