In case it takes a while for someone to get a Y specific answer ...
In my model 3, I put a 12" long strip of hook & loop tape (aka velcro) around each of the three lower child-seat-latch bars. Leaving the slack under the seat-backs and sticking into the trunk. I strung a 1"wide 12'long nylon webbing strap through those and leave in along the sides of the trunk. When I want to secure something, I put it down, push it towards the seats and buckle the strap. This keeps cargo from sliding back when I accelerate. As you realize, I rely on the seats to keep cargo from sliding forward during braking.
Alternately, I suppose could drive slower.
I've seen products on amazon for making attachment points, but they rely on drilling into the metal, which I didn't want to do as I don't know what's where, what effect it might have on water/rust intrusion, and I don't know how to best position anchors.