Width is always for the widest measurement of the body...doesn't matter if it is a car, truck, bus or RV. Mirrors are subject to adjustment and depending on said adjustment, could change the measurement by a foot or more, hence the universal use of body width. The exhaust pipe's length of projection is also variable, so, it isn't included in anyone's specification listings either. The exhaust system is done by the chassis builder and is "standardized" for that chassis, it is the coach builder that determines how wide a box goes on the chassis and the width of whatever box is set on it, whatever is left over is the projection and is not included in the specification of the vehicle, either in width or length if a rear outlet is used. My DP is 41' 11" in the specs, but, that doesn't include the projection of my exhaust or ladder.
Height is given for the vehicle as built with standard equipment, at proper ride height on the tire it came with. Any changes to that equipment, either be it larger tires or rooftop equipment will change those measurements from the stated specifications. If standard equipment is a standard A/C unit and you elect to have an optional heat pump installed, then the original spec will be wrong for height since most heat pump units are taller to accommodate the dual purpose heat exchanger.
It falls upon the purchaser to make sure that if inches count, that the actual vehicle be measured in the critical dimensions. Coach vehicle builders (actually all vehicle maker's) also include, in fine print "specifications may be changed without notice" to allow for in-model year changes, further putting the onus of checking before buying squarely on the purchaser.
Don and Bronwyn
Down to 1 cat now; J-Lo
2014 Tuscany 40RX
2015 Jeep Cherokee Trailhawk towed