Let's take the words bus or coach or motorhome out of the conversation and insert the word car, which also happens to be privately owned and registered in your name. If you drive anywhere in your car in the course of your business or employment and take the allowable deductions it still does not make your car a commercial vehicle, so if that is correct how is it possible to change the rules just because our motorhome (coach, conversion, bus) is used in the exact same manner? The more you say the more likely you are digging yourself a hole.