Best sliding hitch recommendation

Do people go by rear Axle weight rating or vehicle weight rating?

You bet.
You see those one ton drw trucks with dot numbers on their door pulling heavy GN trailers. We legally/safely load our trucks or trailer up to the vehicles gawrs/tire load ratings if need be.
We don't face a DOT overload violation or a lawsuit for exceeding the gvwr based payload number.

Ford may give a F350 srw a 22000 lb trailer tow rating but that doesn't mean all type of trailers.
I haul cattle/other stock with a 36' triaxle GN trailer with 7k axles. I load the young stuff up front over the truck and heavy stock over the trailers axles or just aft of he axles. This allows me to load the trailer so it doesn't exceed my 2500 Dodge/Cummins rawr.
You can't do that with a fixed hitch weight from a rv trailer...especially a 22000 lb 5th wheel rv trailer.
You have the truck so drop by your local CAT scale and weigh the trucks separate front and rear axles.
Simply subtract the rear axle number from Fords 7230 rawr. From other Ford owners weight reporting your trucks rear axle may weigh in the 3400-3500 lb range leaving around 3700 lbs for a max in the bed payload.
Some with heavy trailers or a heavy truck camper with one ton srw trucks go with 19.5" tires and wheels and rear suspension help.

Anywayz get those axles weighed.