I think it's a good business model, especially if you can coordinate time and place with your work schedule and your customers. IOW, if your travels are on a schedule, you will have more repeat business. It will certainly help to be in areas where there are the most customers, places like Quartzite, Yuma, or any of the major areas that RV's flock, also.
One of the good things about a repair business like this is that capitalization costs are fairly low. An extended set of tools and a small inventory would probably get the business launched. A downside is that ROI is going to be meager for the start-up. I could be wrong on that, the OP may hit a "honey hole" of customers but it isn't a "get rich quick" situation (I think the OP knows this).
I would inquire with the RVIA certification folks and see if they have any information for you. I would stay away from any RV repair schools unless you have the time and money and they are affiliated with a certification program.