I know Ford has a grid of each model and trim and shows payload for each. It's up to the consumer to do the math. The manufacturer has no idea what you will add in terms of people, pets, rv's gear etc.
You will need to know the pin weight of the RV's you are looking at, or as a worst case, take 20% of the RV and what you think it will be loaded for travel. Some of it is a guessing game when you are buying because you won't have actual weights until you actually get the thing. I went with the F350 over the F250 mainly because it had greater capacity and the cost was not really any different. I'd rather have too much truck and expandability in terms of buying a future rv than be really close and have no wiggle room.
