pnichols make one good point regarding inner fender wells. I suggest buying a tire monitoring system that monitors pressure and temperature. I unfortunately have the voice of experience in this matter. One of my inner duallies blew out on I-70 heading toward Denver at 70 mph. If I had my TPM system installed that day I would have seen the temperature raising and an alarm would have gone off. The damage was tremendous beyond belief and thousands and thousands of dollars of damage.
If a rear tire blows out at highway speed it will take out both the front and rear boxes and everything inside of them. I also had my propane line severed, broke 4 batteries, destroyed my inverter, damaged my body. I installed much heavier gauge material for my compartments and sprayed foam insulation between inner fender cover and the exposed side of the boxes and as I said, installed a Tire Pressure monitoring System. Tires have a shelf life and it is 5 years. Check your build date code on each tire. If they are 5 years or older, it would be wise to watch them closely. Also look for any sign of dry rot. It could show up on the sidewalls or between the treads. Mine was so slight it was only visible in the brightest sunlight. Enough said!