It sounds like you aren't wanting to pack lightly, so best to figure worst case weight. You will have to use the GVWR of the FW as the total weight. The pin wt will be 20-25% of the GVWR.
Load the truck with the people, gear, pet, and fuel. Go weigh the truck, especially the rear axle. Don't forget to add 200 lbs for the hitch, if not installed yet. Now compare truck GVWR to trucks total wt. How much is left for payload?
Compare the trucks loaded rear axle wt, to the trucks RAWR. The difference would be maximum pin wt of the new FW.
Jerry