The companies that sell packaging material usually stock very thick wall tubes up to about 4" in diameter. They will cut them to any length, or you can easily make clean cuts with a thin "Japanese style" saw from a home supply store. They also can supply plastic caps for the end. The ones I use have wall about 7mm thick and my 100lb helper can stand on the sides without collapsing it, and what that sight that is. Have never had an insurance claim from those tubes which seems like a small miracle in contrast to shipping large, framed pieces.