I didn't do ground vehicles, so I can't give you the intent there.
Before we were doing RIgger 5, I was working on vehicle stuff for myself, and seating was one I kept kicking around. My version was probably too fiddly, and I was using the classic "Body is your mods" way, which is different than the actual designer went with. I had:
Bench Seat
Bucket Seat (Standard)
Bucket Seat (Large)
Bucket Seat (Troll)
Bucket Seat (Dwarf)
Rigger Cocoon
There should be one or two more in that, but this is off the top of my head. Bench seats let you squeeze another person in (as long as you were friendly), but the middle position didn't have a seat belt and being cramped wasn't fun. Buckets were normal in the front, and you could replace one bench with two normal buckets, or upgrade a normal bucket to a Large at a smallhit to your mods (1) ... Troll-sized seats required you to remove a seat entirely (Either the passenger seat for smaller cars or to convert the back bench to a single bucket on the passenger side) Dwarf seating took up a little *less* space, unless it was for the driver, since additional gear would be needed to convert it to one that they could drive.
Again, a tad fiddly.