FrankShore wrote:
You can't and should never use passenger car tires on your RV!
Try some Maxxis tires like suggested and don't worry about filling them with anything than plain old air.
From all that I can gather, when using a P metric tire for a trailer application, the user must decrease the "load capacity" as stated on the tire sidewall, by 10%. If you can still support the load the trailer will place on that tire in that position, and still have a reasonable reserve factor, then using the P metric is within the guidelines.
Me personally for instance on my lightweight ( 4000 pounds total ) camper, with tandem axles, I could use P tires and still have a LOT of reserve weight capacity. I would personally choose them before I would use any ST tire.
As it turns out, in my size, there are several "commercial van/light truck" tires available, in load range D, so that has become my choice .