Craig,
Your timing is remarkable! I just finished installing the second of two sewer hose storage tubes on my rig. The first one is about 4' long and is attached to the rear drivers side of the frame, right under the cooling fans and radiator for my basement air. There is a frame that supports the radiator and I was able to use some large screw clamps and fasten it to a piece of angle iron. I used 4" PVC with a slide on cap. The tube angles slightly downward towards the back of the rig for easy removal of the hose.
The second on I just installed is in the propane cabnet on the curb side. There was plenty of room on each end of the tank, so I mounted a 2' piece of PCV using plummers metal strapping tape to the top of the cabnet metal support rails. Real easy, inexpensive, and gets the sewer hoses out of the sewer bay. I am going to add a second 2' piece directly under the one in the propane bay, and attach it with screw clamps to the first one. I carry a 10' extension sewer hose just in case, so I can add it to my 20' footer if necessary. I had to use them both this Thanksgiving at a camp ground near my house.
Hope I explained it well enough for you, if not let me know and try to fill in the gaps....
Sarge