The RV that I grew up with that my parents bought in the early 70's had a small toilet right in front of the door. You could squeeze past it to stand in the shower to the left, but it was easier to step over the toilet to get into the shower. You had to stand in the shower to get to the sink. The curtain for the shower had a track on the ceiling that went completely around the shower. I'm gonna guess that the entire bathroom was 3x4. Your knees where in your chest when going number 2, and I was just a kid back then!!!!
Newer RV's that I've seen are separating the shower, toilet and sink to both sides of the RV with the hall being between them. Some have the sink outside the toilet area. It's very creative, and the size of the showers is impressive, but it's not something you should do for a house.