I like it being "Heavy Duty". I would invest in some flat black paint maybe. In addition maybe drilling a few air holes to help things dry out during storage.
I went with the 5" vinyl fence post attached to the brackets for the 2" receiver hitch on my 2021 Jayco HT 28.5 RSTS I can fit 20' of hose and the end 90 degree adapters. Used carriage bolts so the hose wouldn't catch on the bolt heads and some bungee to hold the endcap on and screws on the other end. A few holes drilled in the bottom for a bit of air to let things dry out as was mentioned. I don't get why this type of thing isn't factory installed...
I like the end caps. Went to Buyers Products website and found them under PVC Conduit Carrier. I will be using this idea with black abs as you suggested and the drain/vent holes mentioned by GeorgiaTrains. Looks good!