A heated water hose makes a lot of sense...up to a point. But know that ANY exposed parts, from the pressure reducer to the spigot or hydrant can freeze, too. It's better to disconnect and drain your supply hose than to risk something freezing that will break...including the input line on your RV.
Many larger RVs have a sheltered "garage" for plumbing connections, but the typical freshwater connection on the side of your rig is pretty exposed.
Add some water to your fresh tank, and rely on protected internal plumbing to carry you through the cold hours.
Also be sure your underbelly plumbing is safe from freezing. My new X-213 is rated to Zero degrees, except that the black and grey dump valves are on the ends of the pipes hanging out in space, not located remotely up inside the heated underbelly. I'll need to add about a gallon of RV antifreeze to the black and grey tanks before using them in cold weather - so the antifreeze is down in the exposed pipes. The same is true of my fresh tank drain. The tank is in the heated underbelly, but the drain valve for the tank is on the end of about 2 feet of hose hanging below the underbelly cover. Doh!!
I'll need to modify that before any cold-weather camping.
If your campground has hydrants, do the campground a favor and disconnect before you go to bed so the park's plumbing doesn't freeze. When you shut off a hydrant, the water in the stand-pipe drains back down into the ground. If they just have conventional plumbing and sill-cocks, and they leave the water on, they are running a risk of serious freeze damage.
Hydrant:
https://www.amazon.com/Everbilt-Bury...91&s=hi&sr=1-1
Sill cock:
https://www.amazon.com/LDR-Industrie...3&s=hi&sr=1-11
You can, of course, really gear up for cold weather and bring heat tapes to protect any exposed parts that aren't protected by the heated hose. A little insulation and duct tape will go a long way to containing that heat and giving you a protected water supply down to about 10 degrees or so.
https://www.amazon.com/s?k=heat+tape...f=nb_sb_noss_1
P.S. Don't forget your outdoor shower. That thin little plastic door isn't much protection against sub-freezing temps. A good practice is to remove the wand and hose from the faucet, drain them and bring them inside. Add some fine gauge bubble wrap between the faucet and the shower door cover, and this will protect pretty well. It also helps to open the cabinet doors inside to allow heat to enter spaces that might otherwise be cold and contain plumbing in or near outside walls.
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