Cold Weather Travel

I would winterize. Take what water you need in separate jugs inside for flushing or whateve. Put some rv antifreeze in the black and grey. DE winteriz3 when you get into stable above freezing temps, Better safe then sorry
Safe Warm travels

Is your motothome set up at all for sub-freezing use, with non-exposed plumbing and a heated wet bay or similar setup? If so, you should not need to do anything special for the plumbing on this trip. I assume you will not be traveling with heat on for your own comfort if nothing else.

cold weather travel and residence are difficult topics. They are so dependent on your unit build, use and proactivity..
Most units with enclosed water, both fresh and waste, with heat on in the unit while traveling in temps above 0 f should be fine. You burn some propane while on the road. Both safe and legal.
We do not know your unit build, so, I would say if your unit is enclosed amd systems heated, take your colder route, or if you are concerned go the long warmer way.

We have many times left SD with our 5er for the south or returned in much colder temps than you forecast. All was well.

. Another thought, cant you find a local rv pro to give you guidance on your rig?

We are heading to Florida from upstate New York on December 9th.

My camper IS WINTERIZED. We will be dry camping two nights on the way. We do use our toilet but I have a jug of RV Antifreeze that we use to flush with until we get out of the freezing weather.

We used bottled water for drinking and cooking.

I just did the drive from Boise to the CA desert last week. I did winterize before I headed out, stopping at a Love's east of Las Vegas to fill the fresh water tank. I'll do the same thing in a few days before heading back north.

I have a travel trailer, so it's a different set up. But, still... it's worth the minor hassle of blowing the lines and using jugs of water to flush to avoid some major damage to your rig.

I'm going to generalize that an almost 30 year old rv is not going to fare wet lines and single digit temps well at some point either thru design or some modification along the way laeving part of the system vulnerable to freezing.
Unless you have a good handle on how the system is constructed and protected from cold weather, winterizing is the safe approach.
Couple hundo in extra gas vs a couple hours and $15 to Winterize and a truck stop shower or 2, I'd go Winterize.