Sorry to read about your experience. It is one posted all to often. There is lots of good information regarding tires on the forum in addition to all the ideas listed above. I am curious. What psi was supposed to be in your tires. According to the information on my TM I was supposed to run my marathons at 55 psi cold. What size tire are you running? Mine were 14's. Could it be that they may have been a little over inflated? That combined with heat, age, weight and the fact that they were marathons
may have contributed to the failures. I had a blowout on the plumbing side and did have a rather thick mud flap there to protect the plumbing. It helped some. I think it took the "shredding" punishment but did little for the impact of the tire hit. I have since learned how to be a TM plumber.
I have since fabricated a steel protective plate. See picture below. There is angle iron similar to what you see in pictures that runs the length of the bottom outside edge of the TM that provides mounting points for the vertical pieces you see in the picture. It has not been battle tested.
You might try a little bit heavier duty tire or go to 15's as some forum members have. A TPMS may not hurt either, even though it did not help me when my marathon decided to be a snake and shed its skin.