Newbe question, Mercury Mountaineer max trailer size

Remember that if the camper is loaded and weighs 4500 lbs., you are looking at about 520 lbs. of tongue weight. You will need to subtract that from your payload sticker and then figure out the rest of the weight in your vehicle. You may find that you are getting uncomfortably close to max payload.
Get all the numbers for all the weights and do some figuring.
Good luck.