2021 Forest River Sandpiper

I have driven on these tires 1800 miles since my purchase of the Forest River 5th wheel trailer in 2021. While driving on narrow country road at 35 mph, driver's side rear tire blew. It had little tread wear and blew the tread/belt off of 12" of the tire with a gash on the interior portion of the tire from sidewall to sidewall. The tire pressure was checked prior to driving the 15 miles until the incident and was at 80 psi per the tires limits. The tires are rated to be driven up to 75 mph so I was way under that limit. Replaced with the spare and continued the 80 miles home. While the trailer was sitting in my sideboard on asphalt 5 days later, the tire in front of the one mentioned above blew! This time it blew the fender off the trailer and across the road. Again the same damage is seen to the tire with about 10" of the belt/tread blown off and the interior portion of the tire has a gash from sidewall to sidewall. Will now be replacing all the tires as this is very worrisome to a single woman driver. I am concerned how I would have handled my 32' trailer at hwy speeds of 60-65 mph. Neither incident caused any damage to other drivers luckily. First tire was replaced by Les Schwab Tires and employee was surprised as the tires looked brand new to him with extensive damage seen. No truck warning lights were issued prior to hearing the loud noise and seeing pieces of tire flying down the road. I am attaching the photos from the tire that blew in my driveway. Tire size: 235/80R18