I never use the 4" steel bumper on the trailer for storing "stinky slinky." The inside of that bumper is rusty almost the day it leaves the factory. Rust is just like rough sandpaper on the thin plastic of the hose. Some folks use the store-bought plastic storage tubes. Others have made their own using PVC drain pipe and fittings or 5"x5" vinyl fence post stock. My personal choice is a plastic tote box (Rubbermaid or similar) - full length and width, but the shorter ones that are 8" tall or so. I have one devoted to black and gray water hoses, fittings, etc. Another is for propane hoses and adapters and more, and a third for fresh water only hoses, filters, and fittings. I just got a fourth one that is used to store bungies, tie-down straps, rope, etc. The tote used for black/gray water can be kept sweet smelling by spraying a 10% mix of bleach & water on the hoses and fittings inside before closing the lid.
Also, I never let "stinky slinky" lay on the ground or concrete at the dump station. Concrete in particular is just like sandpaper and will quickly wear a hole in the hose. Instead, I carry 3 pieces of 4" thin-wall drain pipe about 24" long, and cut in half lengthwise. I can nest them to create a secure cradle for the hose so that it doesn't lay on the concrete. Additionally, if there is a tiny leak in the hose, the drain pipe contains and runs it right to the dump port. If I need extra length to reach the dump port, the lid of the plastic tote box can be used, too.