The ply rating is a throwback to the 1950s. The actual physical number of plies in a modern all steel RV/truck tire is 1 sidewall ply and 4-5 tread plies. The ply rating is derived from the load rating at the ratio of 2 plies to each load rating letter. A Load rating of G is a 14 ply. H is 16 ply. The most important issue is how much weight do your tires need to carry. Each manufacturer will have inflation tables that tell you how much weight a tire will carry at what pressure.
There are only 2 tires marketed as RV tires. The Michelin XRV. And the Goodyear G670. Both tires have had issues. It's usually better and cheaper to just look for all position long haul or regional service truck tires. Favorites appear to be the Michelin XZA2 Energy and the Bridgestone series 280 and 250 depending on size.
Full time since 2007
2003 Monaco Signature