You can consider an "RV Buyers Guide" that generally sell at supermarkets for about 10 bucks. Now, these will NOT evaluate for fit and finish, drive-ability, do comparisons, or give opinions. But, they print data, as provided by the manufacturers, on the various specifications as floor plans, appliances, roof material, holding tank capacities, etc. It's an inexpensive first-start on researching an RV. Otherwise, I think the pricey book/web site you found is the only "ratings" guide out there. My apologies if this is old news.
Bob