Sooo - the primary reason we purchased the Model X was to haul the two grandkids around in their car seats. It is so much easier to put them in, and take them out, given the Falcon Wing Doors (FWD). However, the design of the rear car seat is not amenable to the top strap of the car seats. In a normal car this strap goes through the headrest posts. In the Model X the strap is supposed to go over the outside shoulder of the car seat and all the way down to the bottom rear center of the seat to the top strap latch point. What I found was that the top strap worked it's way down the side of the seat and became virtually useless. My solution was to go to a company called Strapworks and purchased by a 3/4" wide by 2' long strap with 4" loops at both ends (~$8). I put the top strap through the two loops and put the strap around the seat headrest. The strap holds the car seat top strap in place and will not let it slide off to the side. In the event of a crash, the top strap will take the load, as the car seat and latch system are designed. I would highly recommend this approach to anyone using a car seat in the rear seats.