S.D.
I see nothing wrong with a high back booster seat that commutes to diff cars as needed with the seat belt option. I would have him sit in the middle of the back seat..... Anyway, I do agree with the other post. If YOU are not comfortable, then I would not do it. But it was fine with me at 40-45 lbs to use the high back booster with a seatbelt. My kids were tall and it seemed to work well.