So, I solved my problem.
My original caps had the word Camco on them and they were made of plastic and a loose fit.
I went to the local dealer and he sold me a cap made of rubber. It is such a tight fit that I had a hard time installing it.
I didn't want that on the side of the bumper that I removed the sewer hose from so I installed that cap on the other side. Then I moved the other loose fitting plastic cap to the side of the bumper I open most often. I then drilled a hole through the bumper and cap to drop a 1/4 inch bolt into on that side.
Looks like this will work out OK for me. We'll see as the season progresses.