Question about payload on a 2015 pro 4x crew cab and wanting to possibly tow a travel trailer

Hi everyone, I've barely started toying with the idea of towing a travel trailer but everyone keeps saying to be cautious of the numbers and weights which is all fine and dandy but I'm stuck and would like some input. my 2015 pro 4x Crew cab Frontier states that "The combined weight of occupants and cargo should never exceed 882 lbs" So my question is, if the tongue weight is something like 400 lbs, does this get deducted from that total meaning passengers and gas can only weigh 482 lbs total? at 8lbs a gallon, a full tank of gas would then drop my payload to 313.2 lbs which means I leave the wife or leave the kids but they all cant come along. Am I misunderstanding something or is my interpretation correct? I really hope Im misunderstanding something because it can tow a decent amount but it cant actually if this is the case. Thanks in advance Im new to the sub but appreciate everyone's support of each other.