I use Pearl Izumi shorts for everything on a bike, road, mtb, or touring. The synthetic chamois is thin and is important for moisture management, not just for padding. In 1990 I toured for 6 weeks and switched between natural chamois and synthetic and had no problems. Natural chamois has no padding and is for moisture control and to prevent chaffing. It just starts out like a piece of wood until you lube it up. When on that tour I used Vaseline lotion.
I have tried to ride in a tee shirt but I have to peel it off after. Cheap bike jerseys for all rides since that.