They DESTROY most fivers.
Two years ago, I decided that was the way to go; did some research and was told it could damage my fiver. I could not see how, (after all we had a high end fiver that was very well built, and we had towed it 15K miles without problem one ) so we bought and installed a Cody adapter from Quick hitch.
Shortly after installing it we left on a 2500 mile trip. About 2000 miles into the trip, looking in the rear view mirror, I could see movement between the pin box and the body of the fiver. On checking I found that the welds holding the pin box to the frame were over half way torn out; I was with in minutes of losing the fiver.
RV fivers don't seem to be braced to tolerate the stress of the adapters.
Good luck
Vaughn