I bought a dog safety harness with a tether that fits into a standard seatbelt buckle. But instead of sitting on a seat, the hound dog rides in the back, tethered to one of the tie downs. The seatbelt buckle insert at the end of the tether is attached to the tie down ring with a carabiner. She loves riding in the 4R.
How firmly are those tie down rings attached?
RH