I had a Wave 6 in my motorhome and that heater was almost never covered and lasted about 17 years. The heater was rarely exposed to direct wind blasts that would carry dust into the pad. For the last 2 or 3 seasons the heat output was a bit low, probably due to contamination from cooking vapors, dust and impurities in the propane, presumably, or maybe that is about the expected life of the pad.
That the pad is 'very susceptible' is, I think, overstated.
Yes, if it's mounted where it can be physically damaged, or blasted by dust storms thru an open van door, then it might shorten the life, or if you are sweeping the floor, or sawing wood, or painting, or using chemical sprays and cleaners in your van, then I would suggest you cover the heater.
I now cover my Wave 3 in my truck camper ANY time it's not in use because of its proximity to the back tailgate and hatch, I never know when the wind will blast the dust around inside the camper.
Just FYI, the Wave 3 and Wave 6 (and probably the Wave 8) do have keyhole slots on the back so you can lift them off the screws it is hanging on, if wall mounted.
