When I tried to dry fit the lower body/motor tube, I found the plunger was a bit loose and I don't think it is 100% straight. To ensure it doesn't bind, I decided to use actual 29mm motor tube for the bottle section. This is slightly larger and also will let me use small 29mm motors should the rocket's weight grow. Instead of attaching a plug to the end of the plunger, I decided to use a floating piston. This approach will make the alignment less critical. Plus, the forward end of a SU 29mm case makes a natural piston.
The nose and body will be connected with one shock cord. The parachute will attach to another cord, which will be attached at the tip of the nose section where the squirter's nozzle is located.
That's the design except for the fins. I have no idea of what to do for fins. Hmm, I wonder what pre-cut basswood shapes are in stock at Michaels?