When doing a lot of driving I like to stop at least every 4 hours....that is barely a half tank of diesel for my 2018 Ram. I have never had an issue with the tank size. For a break after driving 4 hours, I like to stop for a while so the time spent refueling is not a concern. I typically refuel, use the restroom, spend a few minutes in the camper checking emails, planning routes, and just plain taking it easy. I often take a short nap.
After a decent rest, I am ready for another 4 hours. In the Summer when the days are long, I often do a couple of rest stops and feel relaxed and can easily handle 10-12 hours of driving. If I try to avoid or shorten my rest breaks, I feel beat up with only about 8 hours of driving.