the manufacture posts a GVW/GVWR, which is a number based on the engineering factors and the axles and tires installed at the time it left the factory....
there is also a manufactured vehicle/trailer DRY weight listed somewhere, but the actual dry weight can vary by several hundred pounds due to last minute changes/upgrades, component weights taken from an average, tire and wheel package, the list can go on, ect...
it doesnt matter if the changes were made at the factory or by the dealer, the actual weight is very seldom within a couple hundred pounds of the listed weight... it needs to be ran across a scale to get the actual numbers. this can be done when you first take delivery of it, and then afterwards when you have all tanks full and its loaded with everything you will be traveling with...
only then will you know if you are exceeding the GVWR... heavier axles or different tires could increase the GVWR of it if you find you are too heavy, PROVIDING the manufacture has built the frame strong enough to support the extra weight.. which is not to be taken for granted.
always check with the manufacture....