Two things to understand. the GVWR of the trailer is the maximum weight of the trailer AND anything in it.
The GVWR of the tow vehicle is the same as above. You won't want those two weights to exceed the CGVWR of the tow vehicle.
You need to know the Combined Gross Vehicle Weight Rating (GCVWR) of the tow vehicle. That is the maximum total weight of the truck and whatever it is towing.
Now, another thing you should know is the pin weight of the trailer. That is the amount of weight resting on the vehicle towing the trailer. It is important because if your tow vehicle may have a GVWR of say, 7500 lbs. If you fill the gas tank(s), put all the "stuff" you want to carry in the bed, put your passengers (and animals)in, you may find you weigh a lot more than you think WITHOUT EVEN HOOKING UP THE 5ER. Say your tow vehicle, loaded as above, weighs 6900 lbs and the pin weight of the 5er is 1500 lbs. You have to add that 1500 lbs to the 6900 for a total of 8400 lbs. That puts your tow vehicle overweight. Now, if your 5er tops out under your tow vehicle's CGVWR, you are still overweight on the truck. Sounds complicated, and it is, but you have to remember that you can easily overload one segment of the combined rig and still be under the gross of both vehicles.
I would look at the Gvwr of the truck, pin weight of the 5er, and the Gvwr of the 5er as well as the total combined gross vehicle weight rating of the combined vehicles.
