I too hate things bumping on the backs of my legs when walking long distances. I have Glenda's innertube seat and I just carabiner it to the belt loop on my right side so it's riding on the side of my hip. Doesn't bother me a bit walking because it's not hitting the backs of my legs.
I wear the satchel so that it is on my left side/left hip, then the seat is carabiner'ed to my right side belt loop. Give it a shot, super easy and comfortable