With all respect, you may want to read some of the tire threads in this forum before you let the tire shop talk you into some cheap "ChinaBomb" ST tires. I doubt the tire shop guys have ever pulled a 5th wheel RV - they are just going by the literature touting the supposed benefits of the ST ("Special Trailer") tire. The LT tires I listed above are recommended by their respective manufacturers for trailer service, and the XPS Ribs specifically are a favorite for the heavily loaded gooseneck trailers used by the hot-shot rigs in the oil fields because of their toughness, durability and long mileage.
The tires I listed don't just have steel belts - the carcass plies are also steel.
Rusty