Fifth wheel shopping question, rear tow hitch

Bionic Man wrote:
...I wouldn’t worry about finding a trailer with a hitch. Find the one you want and have a good, heavy duty, hitch custom fabricated by someone local. The only part of your warranty that could be voided that way is your frame warranty, and it is likely that would only happen if you had a problem severe enough that your trailer had to go back to the factory...

One good reason you don't want the frame warranty voided, is if it isn't heavy duty enough to support the additional weight of a towed vehicle cantilevered all the way off the back of it. Seems to me if the manufacturer won't warranty the frame if you tow with it, it's probably not something you want to experiment with to see if it will work - Just My Opinion.