Yeah....would like to have one to work on the toilet w/out having to run out and turn off the water at the service center. Also, would like to turn it off at the toilet when we leave instead at the pedestal.
I put one on our last trailer because I had a faulty vacuum breaker valve on the toilet. It was spraying water on the wall and floor. I went to a local Lowes and purchased a 1/2" pex valve and installed it. I carry a pex tool and clamps with me for this reason. The Shark Bite as Dave suggested is a good option also. Our 5th wheel was still covered by the warranty at the time. We were able to finish our trip and have it repaired when we got home. We just left a couple of one gallon bottles of water in the shower so we could continue to use the toilet.
I plan to install one on our new Reflection shortly after we pick it up. I carry a couple in my toolbox now.