I carry mine inside the 4 inch bumper. There is lots of rust inside there, but the hose is so thick I suspect it will take years to wear through it.
I've never lost a bumper cap, and even if I did lose one, the hose takes tremendous force to pull it out of the bumper. The little knobs on the fitting at one end wedge perfectly into the bumper and keep it secure. After I pull that fitting out the end, the remainder of the hose comes out easily.
My trailer is 10 years old, and it will easily take another 10 years or more before rust is a problem in the bumper.
