Caleb, right in line with what has been said so far, I also agree that you should FIRST load that baby up like you're going camping. Fill the truck as usual, plus a full tank of fuel, add all your passengers and head out to the nearest CAT scale. There is one not far from where you live, for example exit 71, I-95, and make it a little adventure for the family. You weigh your rig and the family heads inside and puts the big warp on the ol' Mastercard!
You are going to be over your gross payload, probably in the 600 to 900 pounds, if not right now then you will be after a few trips. The excepted number to use when figuring pin weight for 5th wheel RV's is 23% of gross weight. Usually this number will be in the 19% until you've owned it for a year or two.
The posters above have given you good information, and not one of them came in the morning mail or fell off a cantaloupe truck. Take what we've said to heart and then get back to this thread after that pass across the CAT. How you deal with it is your business, but having that knowledge is important.