I sit always, at home and on the road.
On the road it can be a bit of a hassle with busy truck stop restrooms, and me not being fulltime yet, so the men's room can be full, and the privacy in some is a bit shady (Though Flying J's have the best stalls.) But the way I dress does not give me a choice in the matter.
At home I sit just because. 🙂
On a side note though, as some, or all may know it is a tactic of some (most??) truck drivers to use a bottle in their truck when they don't have the time to stop and hassle with a truck stop. I admit I am one of those drivers. So, in those situations I guess I stand. (Though I feel I must also add that any of those bottles you see on the side of the road, etc... do not, and never will come from me.)