Couplers

You'll need a coupler when you need to connect two body tubes end to end. With a outside diameter slightly less than the inside diameter of a body tube, couplers fit snugly inside body tubes to provide strength to the joint betweeen the tubes. With glue to secure them the joint is permanent, but without glue on one of the sides of the joint, you can create a separation point in your airframe for deploying the recovery device.  You can add a bulkhead to prevent ejection gasses from getting into a payload bay.