A bit more info might help.
How is it supposed to anchor and/or index onto the barrel nut? Is there a jam nut, does it clamp down with screws, or are you just supposed to thread it on until it stops? Maybe provide the manufacturer and model?
If it is an aluminum tube, and threads onto a steel barrel nut, you should put something between them, if for no other reason than just to prevent galvanic corrosion. Whether that should be a thread locker, or something like the anti-sieze used between the barrel nut and receiver, would depend on how the tube is supposed to get locked down.