Is this your first large mh? If yes, and with all due respect, it may be you that is causing this problem. First time large mh drivers tend to over correct during normal driving by looking at the road too close to the front of the mh. Looking further out (like you do in your car) will eliminate the wandering.
If you are an experienced large mh driver, then I would guess that the steering and suspension on the front of the motor home needs some expert adjusting. Being 17 years old, a lot of things could be worn and in need of replacing and/or adjusting.
Ron