I have always changed any flat tire I have had the pleasure of getting but I have been able to at the time with the prerequisite tools and a spare tire and the tire sizes I have been able to manage. If you can do it why not. However there are some you may not be able to change simply because you don't have the proper tools or a spare or you physically cant do it because the tire is too heavy. A trailer or fifth wheel should be no real issue to do it yourself assuming you have the proper tools for the job. Class B should be no issue. Class C might depend on which tire or tire size. Class A now you are getting into tire sizes that are just down right heavy to muscle around by yourself. They can easily be well over 100lbs tire and wheel.