Nada is a good resource, but demand is thru the roof due to COVID. Dealer inventory is at an all time low and the factories can't keep up with demand. The flip side is that you can ask a premium price for your RV too, so it's all relative.
RV Trader website is a good resource, you can look up the make/model B that you are looking at locally and see what other similar ones are selling for around the US.
You should also run your class A thru NADA as well and get an idea of what they say it's worth, then look up your model on RV Trader and see what they are selling for. That should give you some idea if the seller's "asking premium" is reasonable in this market.
Never hurts to go look at it, if you like it, offer what you think it's worth. There are a lot of variables like low mileage, stored indoors, new tires, transferrable warranty, luxury upgrades, etc., that may justify the asking price.