OK, thanks for more information, as it helps us to help you.
For planning purposes, when my husband and I had a rig similar to yours (we had a diesel pick up towing a 27' 5W), we had an unwritten rule for ourselves that we would not try to travel more than 450 miles per day, and less than that was better. If we had any plans to stop and sightsee along the way, we would ensure that we had less mileage to drive.
Staying in Walmart and the like ... well, these days, don't count on being able to do that. Too many now have signs against overnight parking of any type. You are actually better off staying in a truck stop/travel center, but ask in the store where you should park. Then it's polite to give them some sort of business, by filling your fuel tank, eating in their restaurant, or similar. As a solo female, the truck stops are probably a little safer anyway since they are used to people being there at all hours of day or night!.
Donna