Track bar

yes. Trac bars are for controlling tail-wag caused by what is being towed.

A track bar will cure tail wag whether or not you tow. Tail wag is caused mostly by the leaf springs shifting a fraction of an inch side to side. Because of the long overhangs most larger motor homes have, simple geometry greatly amplifies the motion.

Ford started several years ago installing a track bar on the front axle because of the axle shifting issue. Why they did not put one on the rear at the same time is a mystery.

Put one on. You will not regret it.

I notice you asked for sway improvement. Sway bars which you already have, I think, are for that. Yes, track bars help with the tail wag. There are a lot of posts on this an other sites on this issue and I have read many of them in recent months. We bought a Baystar several months ago and purposely took a test drive on a very windy day. It didn't handle too bad and decided to go for it, but wanted it better. I read a lot on the CHF. I did the front first, then rear and I just added a track bar. All have helped and it handles much better now. Looking forward to see if the H load range tires I just put on front will help even more. I'm doing this on a four year old coach btw, not a 2017.

Go for it, it will improve things whether you tow or not.