You can purchase them here: https://www.dwincorp.com/product/super-slider-adjustable-super-tube/
Interesting to see on their website that they picture it with a Rhino hose snaking out.
I forgot to add a second hose tube on my trailer order so I ordered the super slider tube.
You really want to get the tube from Escape - the super slider droops and tends to catch the sewer hose when putting it in /out. The one piece tube is much better.
D&W also sells the one piece tube like Escape installs but the shipping is a killer.