I just can’t make the math work on a 5th wheel of that size. Even using 20% of the 5th wheels GVWR for the hitch weight consumes nearly 100% of the payload. I guess it becomes a matter of believing/knowing the vehicle can handle it versus being within specs?
Gvwr and gvwr based payloads aren't used to determine how much weight a truck can safely/legally carry/stop/start. Gvwr and its payload are more of a marketing thing and not a good indication of a safe trucks load limits.
Example a Ram Body builder website shows 2500 Ram 6.4 hemi crew cab tradesman with 6000 rawr has a 3530 lb payload. This trucks rear axle can weigh in the 3000 lb range...now add the 3530 payload = 6530 lbs for a 500 lb overload on 17" wheels and tires.
Same Ram body builders guide shows a 3500 SRW crew cab tradesman 7000 rawr has a 4530 payload. A 3500 srw rear axle can weigh in the 3200 lb range...now add 4530 = 7730 lbs for a overload.
Ford and GM also have the same issues with certain high gvwr/high gvwr payloads trucks and their rawr numbers.
And lets not forget Fords F350 srw with a 10000 gvwr or a 11500 gvwr for the same "identical truck" with different gvwr payloads.
My numbers and examples are just to show the OP (or anyone) how really silly the gvwr game is played...and one reason using the trucks rawr will keep us safe...no over weight tickets....no civil lawsuits we read so much about on rv websites.
Just stay under the trucks (any LDT) gawrs ratings and you won't have any issues.