Re: E350 tow hitch
The members who have commented above are very knowlegeable, so this is just to possibly add data, not to contradict anything.
I have no idea what your frame looks like underneath, but for a while I was looking at ~24' Class C's (E-chassis), and I also tow a boat. There was a hitch put on by the RV mfgr, but it was only attached to the frame extension they had put on, which was not as beefy as the Ford frame. So it was not rated very highly (and some folks had had issues in real life). A couple of owners had had welding/hitch shops improve their installations, and I happened to see a couple of them in real life. Many ways to skin the cat, but the one I liked incorporated a steel beam that went across between the Ford factory frame members (so this was about 9' forward of the rear bumper) and then the new hitch bar came back from the center of that. Super strong looking, yet simplish, and almost all of the hitch weight went to the original Ford frame, not the thinner looking extension. There was a little more to it than that at the rear (I mean the long beam coming back was not just free floating), but that's the main idea. I don't think it was very expensive to have done. Just a welding shop that understood hitches/vehicles.
Some extensions (ones you use with a regular hitch) de-rate the towing capability (of the hitch, not the vehicle). Some I've seen cut it down by 50%, IIRC. So keep an eye out for that. Granted, your (current) boat is light, but still... nice to have a capable hitch, I think.