I have only had to work on one other Majestic 23, but I doubt that your is very much different.
The only worry I would have were this coach mine, I was traveling in sub-freezing weather would be the gray tank. That would only be if it had contents and the weather was sub-teens. In that case, yes, salt will do. The black tank is protected from freezing by the contents. So, you are safer if you use it with as little flush water as possible.
I will forward the advice that I was given when we first had to travel in the north this time of year. It proved to serve us well.
=> Have provisions onboard for three days. It is very easy to get weathered in for a day. If you get stopped at all, it could easily be two days before you can continue. Given that case, you have a self-contained unit. You should have propane, water and fuel for at least that long.
There is a near zero chance that you will find a campground with water and electric, that will matter if you don't have a generator. The house bank will be hard pressed to run the coach heat overnight. That means you may need to idle the main engine for a long time just to get through the night.
Good Luck
Matt