So my truck was ordered without the rear seat. Later Dad built a framework that a factory seat mounts to. That framework has tabs that dop over the eyelets he bolted to the floor. At the rear eyelet, after the seat frame's tabs are over the eyelet, add-a-link chain links with the seat belts looped through them goes through the eyelets. This both holds the seat belts firmly to the floor, and also doesnt allow the seat to come up off the eyelets. My only gripe is that even though it just takes a minute or so to yank the back seat, it leaves the truck with these ~1.25" tall eyelets that catch and snag everything. When camping its ok, the airmattress seems to be unaffected.
Sorry, no pic of the seat in-I'll take one if you think that'll make more sense.
Erik