Remember that the NADA value is coming out of the "National Auto Dealer's Association", and their resources are placed into automobile and light truck price analysis. The person establishing values has probably never spent one night camping or seen an RV. The posted values are just a work of fiction.
Since there are no established chains of RV dealer auctions, there's also no source of wholesale and retail prices available in the U.S. There's no information to analyze.
A better source of the value of an RV would be EBayMotors.com or RVTrader.com. You're looking for a bunch of sales listings for comparable trailers/motorhomes so you can see the posted sales prices. Then you'd need to discount their list prices for what you think they'd sell the RV's for.
And taking a % of MSRP is not that accurate. Not all manufacturers have the same cost vs. MSRP differential. And who knows if they offer some dealers larger discounts for volume ordering/purchasing. Actual cost may not be apples and apples at every dealership.