I have a 10 year old KZ Frontier 28 foot travel trailer that I've had for 7 years now and in the last few years have had a blowout (or 2) on my annual long distance 800 mile trip to Florida from Texas...
Just opinion here, but if you are blowing out every type and brand of tire you are trying, then something else is wrong. Most likely overloading and/or under inflation. With your trailer, is it a possibility to do an axle flip to gain clearance in order to go to 16" tires ? Once you get into 16" you have a much greater range of options that should cure your problems.