I guess you can tell from some of the replies that there are two sides to maintenance.
First is the annual cost of normal preventative maintenance (oil changes, lube, filters, radiator flushes, tranny fluid changes, tires - you get the picture). These are usually on a schedule and more or less predictable based on mileage or time, whether you do them or someone else.I usually budget around $1K annually for the above. I have a local shop do these things as I'm not very handy mechanically.
Things that go in the "house" part I can manage as well as the exterior (seals etc).
Second are the unexpected things that may go wrong. This year I've had to replace the lift pump in the spring before my fist trip, the bathroom Fantastic fan had issues, the water pump (on the motor) went in the fall after my last trip and its in the shop now for "self-inflicted" body damage repair. I did have a $5K reserve fund for the unexpected things, though it is pretty well depleted after this year.
I purposely exclude insurance and deprecation from my annual maintenance cost. When I go to sell, what I get will be "found" money as the MH is paid for and is not an investment.
HTH
Chris