Pray, another idea occurs to me, that I was going to write in response to your PM, but decided to post the idea in public, so that others can shoot it down if they have tried it already without success.
In your travels on the highways and byways of the USA, I'm sure you have encountered "hot shot" less than truck load rigs, typically Ram 4500/5500 chassis cabs pulling gooseneck or 5th wheel flat bed trailers. You may have noticed that some of these tow rigs not only do not have pickup beds... they don't have any beds at all. Basically they have just a 5th wheel hitch spanning the otherwise bare frame rails, with maybe a tool box for load chains, or an extra fuel tank, or perhaps a sleeper next to the cab, but no bonafide bed. Not even a flat bed.
There is a reason for this. These operators want their 550 / 5500 light medium duty trucks to be legally classified as "tractors", instead of motortrucks, which enables them to meet some DOT or FMCSA regulation regarding the overall length of the combination of vehicles, which permit them to tow a little bit longer of a trailer, to accommodate more load, or more variety of loads, per trip.
However, even without a bed, they still need to have mudflaps, per regulations.
And to prevent their rear tires from rooster tailing water, mud, snow, and debris all over the front face of the open loads on their trailers, especially if they don't have a full width deck on the neck, they need more than just mud flaps. They need fenders.
The trucking accessories industry has accommodated this need with many options to choose from... DRW fenders for light trucks that have a curved radius matching the 29"- 32" overall diameter of light truck tires (most commonly, the 225/70R19.5, which is about 31.5").
Keep in mind, the Class 6-7-8 overall tire diameters are 40" and higher (on 22.5" and 24.5" wheels), so the existence of rear tire fenders for Class 4 and 5 "tractors" is a significant enabler for what I am going to suggest that you consider next:
Internet shop for "hot shot" trucking fenders, and carefully note the dimensions with each iteration that you find. Every Class C manufacturer is different in detailed execution, even while they appear somewhat the same at a distance from brand to brand. Same with the fenders that I recommend that you examine. They all do the same thing, but the exact dimensions and mounting schemes are idiosyncratic to the brand.
Compare your measurements of the various hot shot truck fenders you find, to the envelope of space available under your particular Class C. I'll post one or two photo examples of the type of fenders I'm talking about below.
The goal is to keep a tire blow out from taking out other equipment under the coach, which in your case was a grey tank (and would be in my case too, if I ever had a blow out). By putting a sturdy barrier between the dually tire pair and the coach bottom, it seems reasonable to assume that any ancillary damage from a tire blow out can be better confined.
(I have no affiliation with the images or companies posted above. I simply did an image search of "hot shot dually fenders" to present some visual examples to offer clarity in my suggestion to try and tuck one of these suckers inside the larger more rectangular wheel wheel space under the motorhome).
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