In two years of full timing, we had two problems with our diesel pusher, a fluid leak, and a blown turbo. Our leak fix in Texas was a day job. The same spot leaked a second time. We got it fixed in Denver and had to stay overnight in a motel. Our turbo blew just outside NYC. This was also a one night motel stay.
I agree with the other posts that routine maintenance will prevent lots of problems. Sometimes though, stuff breaks.
Our diesel pusher had a caterpillar engine. We had all our work performed by Freightliner Truck service centers. There was simply no way to camp out at the shops, or have them come to us at a campground.
You just need to plan and budget for the occasional repair job.