Mobile mechanics are a great way to have maintenance done on an RV. We've begun to use one for service of both our 4X4 pickup truck and our Class C motorhome chassis right here in the mountains in our backyard - and we may try another one for the coach part of our Class C RV.
One is an expert on maintaining the Ford E450 chassis, and the other is an expert on maintaining trailers, mobile homes, and the coach portion of motorhomes.
Moble service guys have to be good or they wouldn't last long ... plus when they come to where your RV is you have their whole attention just for your job. There's no need to have the RV setting somewhere waiting for someone - out of perhaps several mechanics of varying skills - to eventually get around to it.
I'm all for the mobile service guys!
2005 E450 Itasca 24V Class C