Well Zippy,
As we don't know what you will be driving, there is no way we can guess how long you will last. We can easily do a 600+ mile day, but one good museum can shorten the day by a lot. But, if the ride is not comfortable, there is no way you will last that long and if you are the only driver, that shortens things even more.
I suggest you buy or borrow a copy of Street Atlas and learn to use it. Then, carry it with you and keep it up to date. If you load it with your real length of day and fuel numbers, it will tell you where to look for someplace to sleep and the same fuel. We even load the times we expect at the stops like monuments and museums. (These are always wrong, but they are close.) That and GasBuddy make travel much less stressful.
Learn to work the new stuff. It is easier than working.
Matt