Is your motorhome a Ford F53?
Mine starts smelling like that every 3 years or so,because this era of Fords front and rear brake calipers need to have the slides on the calipers lubricated with high temp grease every year I think.
The smell on mine comes from the brake caliper piston boots starting to melt from the heat from caliper not sliding freely. (because I won't pull the wheels off once a year myself)
It's not easy jacking up the motorhome and removing wheels and my braided stainless brake lines.
I find it easier to replace the brake calipers very 3 years or so. I don't recommend others do it this way though. ;)