The dry weight is not a very useful number. This is generally the weight without any items listed as an option, like A/C, microwave, awning, batteries, TV, etc.
There is no correlation between gross and dry weight. The only way to know the weight of the unit is to run it over the scales.
Depending on the age, there may be a sticker inside a cabinet proving the weight as it left the factory.
Amateur Radio Operator (KE5DFR)|Full-Time! - 2012 6.7L Ford Crew Cab Dually -2013 HitchHiker Champagne 38RLRSB - Travel with one Standard Schnauzer and one small Timneh African Gray Parrot