I'm turning 70 years old and have bought a lot of tires of different brands, but when I replace my RV tires I only look at Michelins. I'm surprised you have cracking in the sidewalls of your tires on a 2010 model RV. Either the previous owner left it parked in the sun a lot or the tires were old when they went on the RV. That said, you might want to talk to someone at Phoenix to get their thoughts, as the way the RV rides is not just the tires, but the springs, shocks, antisway bars, etc. Since RVs usually call for high inflation pressures, I suspect a change in rubber compound in the tires is not going to make a big difference in ride. Anyway, good luck in your tire buying efforts. I've neglected that in the past and had to buy one on the road and it's never cheap when that happens.
Jerry