SteveR runs from KC area after Christmas and runs with water, heck they are fulltimers, they are gonna have water.
We take the other road, will leave here, God willing, a day or so after Christmas, the last 2 years it has been 4 and 4 below when we pulled out. Call us lazy, but there is no way we are gonna pull out hoses from the frozen tundra and sheds, hook up, fill up, and then have to drain all that water and drag back into the frozen tundra and sheds. We run 2 to 2.5 days without water till we get to about Arkansas. We take lots of baby wipes for cleaning up, and a couple of gallons of water for flushing. Not the most fun way to run, but it works. We do run with heat on about 45 degrees cause ole Carol's violets and houseplants are in Tana's greenhouse (shower). We stay in campgrounds, not in Flying J's or Walleyworlds. If I ain't gonna have water, at least I want POWER!! (Which also translates to Carol wants her coffee each and every AM and she no longer carries a pot that works on the stove, POWER, give Tana POWER!)
If you have no dogs, or maybe one dog there are hotels/motels you can stay in the first day or so out of Montana. We have friends that leave the 26th, EARLY, every year, they run like the wind and are always in the Rio Grande Valley by the 31st. The first night or two they stay in hotels. They have no dogs. Nothing wrong with that approach either.
We usually do not unhook from the time we leave here till we arrive in RGV. We take a full frig, for breakfast and dinner, and eat a big meal at lunch in a truck stop or where ever we are for lunch time. I make up foods that suit us for that type of meals, a quiche for the AM, heat in the Microwave, really gives us a good start on the day. Evening meals are soup and fruit and maybe some sandwiches and yogurt, whatever sounds good. If we need to refill the frig, we stop at good ole Walleyworld and do so.
Ya do what sounds like the most reasonable plan, what you are comfy with, what works for your family. I might be jealous that you are leaving the 15!
Have a grand time and safe rides!