"but if we can’t depend on ANY numbers from the vehicle or the RV manufacturer to be correct,"
What, you're frustrated by the answers you are getting here? That's all part of trying to figure out weights, that's for sure.
I would say, "no", you cannot depend on numbers the RV manufacturers post. They all use a weight of the base trailer, with no options or additional equipment. They then weigh the tongue. Again, stripped. Not real-world numbers, in any way, shape, or form.
The best way to figure weights is to get the actual weight from trailers with your configuration, as they sit on the dealer's lot. The white sticker tells you the weight of the trailer as it left the manufacturer's lot. But, you still have to add batteries, water, and all of your stuff. That's why you have been advised to use GVRW of the trailer. However, you said the model you are interested in has (somethin like) 2,500 lbs of cargo capacity, and you won't use all of it. You say you have about 850 lbs of stuff, which does not account for water, batteries, etc. If you add water weight (you never know if the water will be available where you go, unless you always go to higher-end facilities, as there are water outages occasionally that have no backup plan), and 1,200 lbs for your stuff plus batteries, etc., that will give you a better "loaded" guesstimate than using published dry weight.
As others have said, use at least 13% of Gross Wt for tongue wt. You have no idea how the load will balance, compared to dry wt. Using the 10.7% tongue wt of a dry unit is assuming all loads will balance the same way as an empty trailer. Bad assumption. Err on the side of heavier tongue, so you don't find out most of the loaded wt is on the tongue.
Don't try to squeeze a trailer into your desired weight range. Be realistic with projections. I see others post questions, and the vast majority of the answers are not what they want to hear. Then, when someone says "yeah, my buddy tows with the same rig, and he is over the weight limit, but he has no problems", they jump on it and say "Thanks for letting me know it is okay". They ignore reality, to embrace only what they wanted to hear in the first place. Not good when your family's safety is at stake.
Good luck!
