Most RV's GVWR is dependent on the POS tires that they have installed when being built.
Sometimes it's only adding a couple more bolts to the kingpin that can change the rating for example from 19-21K.
Bottom line know your actual weights on the RV tires and axles. Just because it says 21K like my RV does does not mean you magically stop increasing in weight at 21K. My RV weighs 23K. I added stronger bolts to the Kingpin and my tires still have plenty of capacity I am over my 8k axle ratings but MORryde said I am within their specs even at my 8,750# per axle.