You should contact your dealer and find out which welding shop they recommend. Just adding a receiver to the bumper will not work. However, there are several important considerations before you move ahead.
Adding a hitch will likely void your frame warranty. Any problems that would have anything to do with pulling a trailer behind your rig will no longer be covered. If you are out of warranty, then it’s all on you anyway.
Many states do not permit pulling a trailer behind a 5th wheel. States that do have overall length restrictions from 65’ to 70’ overall and there are time-of-day restrictions in some areas.
There are horror stories about all kinds of problems with towing a trailer from bent frames to cracked walls.
I’ve seen many people towing trailers behind their 5th wheelers and a few friends who do as well. It is done all the time without anything unusual happening. I don’t know how frequent owners of your rig do this but your dealer might know. My dealer was very helpful to people who wished to tow a boat behind their 5th wheel and directing them to a welding shop that added additional support as they would do this to used rigs no longer under warranty.