The tubes in my cage? They're large diameter (I have big squishy boys) dryer hose.
Bendable and such. I got 5 feet, I think, cut it in half with tin snips, but you could leave it whole. Attached to the sides of the cage with paperclips... zip-ties would work as well, or shower hooks or whatever you have.
My older boys chewed 'peepholes' in theirs, but nothing more. They seem to like sleeping in them and climbing on top of them.