This right here is what a lot of people don't understand about RVs. Most of the weight in an RV is fixed weight - you can't move it around. Sure, you can put your clothes, dishes, food, and other paraphernalia in different spots and change the tongue weight some, but for most* RVs it won't be enough to alter the weight you're putting on the hitch. They're not flatbeds where you can control where the load is sitting, they're a house that has been laid out and built a particular way, unless you can move everything around inside you're not going to make a huge change.
* - this comment does NOT include toy haulers, where you can load up to several thousand pounds in the back. Toy haulers are the exception to the rule, since adding 2-3k in the back, behind the axles, is most definitely going to alter your hitch weight. How much, once again, depends on the layout of the trailer.