Last year I replaced the tires on my Outback 298RE with Carlisle's (ST225 / 75 R15, Loan Range E, 80 psi, rated at 81mph ... all labeled right on the tire)
Even though I had only 1 bad tire (factory original), I replaced all 4 at the same time. Since the tires were installed, we've made 1 trip to Florida and 2 trips to South Carolina (from central Indiana), and several trips across Indiana. I keep the sun side of the trailer tires covered at home all the time. The shadow side is not covered.
I've had absolutely no problems with these tires. My speed is normally 60 mph, 65 at the absolute fastest, and I am very careful when backing that I'm not forcing side pressure on the tires by backing in sharp turns. Not always possible, but I try very hard to avoid backing sharp turns causing side force on the tires.
For the size of your trailer, these Carlisle's would do you very well. Get all 4 tires the same, whatever you do, and replace all 4 at the same time, regardless of how good the remaining tires look on your camper. Treat your tires the same as you would on your car or truck.