Fickman,
I'm going to give you my popup story. Bought a used popup (10 years old) that was in great shape. Tires all looked great. Not a crack, blemish, bulge, blister or scratch on them, good tread depth. Took it on a couple local trips, less than 70 miles. All was well. First week long trip planned, going to the smokeys, 5 hours away, get up at 6am, leave at 730am, on the side of the road at 830am. Blew a tire, tore up the bottom of the popup right above that tire. Tire changed, gorilla tape applied, onward we go. Enjoyed the trip, get home, start reading about dates on tires and go check mine and find they are 5 years old. Took the tires off, bought some new ones and had them mounted and balanced and lived happily ever after with the popup until she was traded in on the TT I have now.
Stick with the ST's or go over kill with the LT if you like but change the tires. 5 years are ticking time bombs and tires that blow at highway speeds can do a lot of damage to plywood and vinyl flooring found in most popups when they go.
Maxxis Tires at Discount Tire