Yes, by all means replace. Recommendations are to replace at 5 year intervals regardless of miles on tires. I replaced our originals (trailer tires btw, not light truck tires as you have) when they were 6 years old. When we purchased our 177 in January 2011 the tires were already a year old. Replaced and had 20,000 + miles and still looked like new, tread wise. Second set purchased were Hartland tires from Discount Tire, a "C" rated tire. Yes, they are manufactured in China, as are most tires and after 4 years and 15,000 miles, have performed well. Our next set will probably go with Carlisle "D" rated. Many have gone to the Goodyear Endurance.
What you don't hear is when people have tire issues is have they been properly maintained. Have they checked tire pressure? "C" rated is to be 50 psi. "D" rated is 65 psi and you can safely travel at faster speeds than the "C" tire. Some have even gone to an "E" rated tire but some have reported that since it is such a stiff tire, it tends to shake things apart inside the pod when traveling on rough roads.
Replace a 3 tires, even though your spare hasn't been used and is brand new (no mileage) the rubber has still been deteriorating due to age and possibly sun, unless it has been covered.
I change the tires myself. Tire chain stores may or may not know how to properly change the tires on your R-Pod. If they can place the jack as close to the tire as possible while lifting, you will be ok. If they can't or won't, I would do it myself.
I would avoid any L/T tire, go with the safer and stiffer side wall S/T tires.