I've laid white carpet on the bottom of the tube as well, so the tube is very dead sounding now, not a hint of an echo
I had to go crawling to the end of it to fit the lights (felt like Bruce Willis), so I was fully enclosed in the tube, it's very quiet in there.
I'll be welding up the pellet catchers tomorrow, they will also be carpet covered, as will the back stop.
Once the end panel is made to cover the gap, that'll be the tube finished.