you can "tack glue" the tubes together with a small dab of 5 minute epoxy. If you ever need to remove the tube... the epoxy is easily undone by gently heating the tubes. just use a very small amount of 5 min. epoxy.Sweet that works for me, I have more of the smaller diameter tubing. I also did the stuffing box like you had mentioned, just wasn't sure if was suppose to be glued in the stuffing tube.
Thank You,
Paul