Is this a new problem? Did it just start happening?
Our 2009 Jayco Greyhawk Class C (bought April 2009) drove great when we first brought it home. I was very happy with how it handled. Then in late 2016/early 2017, it started to wander a little on the highway. Not bad, but not like it used to be. I took it to a trusted mechanic to replace the tires and asked them to do an alignment. They replaced the tires and told me the ball joints needed to be replaced. I don't remember the exact cost, but it was just under $1000. The parts are cheap, it is mostly labor. After they replaced the ball joints and did an alignment, it drove like new again - maybe even better. Our Greyhawk had just over 30,000 miles when the ball joints were replaced.
If I were you, I would start with an alignment and go from there.
-Michael