IMHO long rides require having multiple subtle position changes in the saddle, multiple handlebar positions for the hands and various riding techniques. I will sit a little to one side or the other or a little up or back if my rear is getting a little sore. I will just stand and pedal for a few minutes to use different muscles, I will change the power points in my pedal stroke to use different muscles - all of this allows me to go for a long time. Even at all that - a rest stop every 20 or 30 miles is a welcome relief.