you either gotta be "handy" or "rich"....
Owning a coach is no different that owning a car & a house...either you fix 'em yourself or you pay someone. even if you replaced everything, MECHANICAL stuff still breaks....even on NEW Coaches too !
Carry tools and some anticipated spares...but you cant take the entire automotive store AND LOWES with you everywhere. I suggest carrying a multimeter & some duct tape too.
If you're not TOWING a vehicle behind your coach you might wanna consider it....its good insurance if you break down or need parts (that you didn't anticipate) even if you're stationary in a campground....w/ a toad you can go get what you need.