Our 31-ft runs very close to its max weight rating. For that reason I went with what I'll call "upgraded" and you call "commercial" tires. The Michelin XPS Rib is one, another is Bridgestone Duravis R250. We chose the R250. Your 21-ft should be much lighter. You STILL need "LT" (Light Truck) tires and the numbers you posted are what you should be getting.
I got ours from Discount Tire and was very pleased with their professionalism and the price.
The Michelin LTX MS/2 is standard from Ford on motorhome chassis, and it's a good tire.
In my opinion, the Firestone TransForce is a very good choice. When I was shopping, it was my top choice, and best price, among the standard tires I'd actually consider running. You CAN find that tire size in off brands around $100 each. Personally, I'd avoid those.