I think I mentioned in your other thread that it would not be all that difficult to make a plate that bolts down to the seat rails. You can span the rails and use u-bolts or j/hook bolts to bolt down to the pins in the rails. Bolt whatever you want to the plate. If you do this the plate will not be compromised by the carpet padding. It should set on the rail tops.The cargo van & passenger van are quite different animals as the cargo area, cargo van would be drill holes.
I am trying to leave the floor carpet intact, will see.
Metroplex did not post how he held down the chaulk, I am looking for something more securely held down & inches here may matter.
Max tensile load on the seat rails is 787 lbf assuming 2 tie down points and 1 meter distance between points.
If you were only worried about forward forces you could tether your chaulk to the seat anchors as shown in the picture I linked to. Two tethers and 4 straps to d rings would probably do it.