Also put a set in the passangers floor, out side edge. If I need to strap something down in either of the back seats and the seat belts are not positioned in the right place, I have the tiedowns in the floor.
I used quick release cargo straps from McMaster Carr (8834T62) that have bolt down pads on the ends rather hooks. I bolted them directly to the floor into 1/4" nutplates that I had installed when installing the baggage floor. The straps are 1" wide and available in various lengths.