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...
Maxxiss are the best your going to find in a ST tire but I suspect there's just too much weight for a 14" tire. So I would move up to the 15's or even 16's if you have room. Also remember to keep your speed at or below 65 with any ST tire.
How many inches of clearance do you have between your tires?