Let's pick a TT at 12K gross. Your tongue weight will be about 1500 lbs, WDH about 100 lbs, 3 passengers at 450 lbs, miscellaneous tools and 'stuff in the bed at 400 lbs. You still have about a thousand pounds of payload to pay with. Remember, you are within safe parameters in payload, but you will be towing a VERY large sail down the road with that gasser.
With the 5th wheel your pin weight will be in the 2650 range, hitch about 200, passengers about 450 and tools and 'stuff' about 400. Now your cargo has been boosted to 3700 pounds, 300 pounds out of cargo capacity, plus any options you've added like air bags, bed liner, bed topper, and the like. If you have a diesel rather than the gasser you can add another 500 pounds to the cargo total and now you're out about 7-800 pounds.
I know it is a dilemma, but you aren't too far out of reach on any of the numbers, just stay under the numbers we talked about.
One more suggestion, log on to
https://www.keystoneforums.com/forum...archid=6833659
with the same credentials you use on this site. Post your question exactly the same and you will be getting a veritable multitude of answers. VERY knowledgeable
people there and all looking to help Tell 'em I sent you...