Small engine repair and maintenance is a practical way RVers with mechanical knowledge can earn a living. There's a definite need for it and the required tools are small enough to carry with you.
Most campgrounds have lawn mowers, weed eaters, chainsaws, lawn edgers, leaf blowers, garden tillers, portable generators, air compressors, water pumps, pressure washers, snow blowers, chippers, shredders, and similar gas powered equipment. Chances are high that those tools need routine maintenance and a good cleaning. It's also likely that one or more of them needs repairs.
Your typical campground owner is busy. He may know that keeping his power equipment in good shape is important. But, even if he knows how to do it, he probably has a hard time finding the time to do it. He'll appreciate a capable RVer who is onsite, with tools, and who offers to do the job.
You may find a surprising number of RVers also travel with some of these. Think portable generators, to start.
Small engine mechanics can do more maintenance than actually fixing. Small engines need regular service and adjustments for optimal performance.
The tools needed for small gasoline engine repair aren't nearly as bulky as a full set of mechanic's automotive tools. You should be able to find a storage compartment to keep them in without too much problem. Skilled mechanics do a lot with hand tools like wrenches, pliers, files, and screwdrivers. If you are mechanically inclined RVer, you probably have many of the basic tools along for when you do your own RV maintenance.
Being a self-employed small engine mechanic is a natural way to earn your living while RVing if you already have small motor repair experience. If you have the aptitude, but lack job experience working as a mechanic, you can fine-tune your skills by taking small engine repair courses at a vo-tech or classes through a community education program.