I added lap belts to my 110 CSW which already had sideways facing bench seats. With these seats there is a big gap between the bottom of the backrest and the bottom. The belts go through this gap so they met the floor well behind the passenger, holding down and back. For three belts each side you need four locations. Each belt has a strap and a clip, for the middle two holes you can stack on the same bolt the clip for one and the strap for the next. For the rearmost ones I drilled a hole through the floor (top of the wheel arch) and reinforced it with an alu plate about 60x60x6mm. I don't think that will pull through! As my landy has the middle row of seats, with belts, it had an attachment point already fitted for the mid row belt, on the sloping bit of floor, an alloy casting under the floor. It was already drilled and tapped with an extra hole for the frontmost rear section lapbelt. I just had to (carefully) make a hole in the floor, this was very satisfactory. When you measure for the other holes dont go too close to the outside of the vehicle or you won't have room for the plate underneath. If you are going to bolt through the plywood as well you may find the bolts could be too short. We mostly use the back seats for kids (though not baby seats) and they are good for keeping them in place, without them they slid about. Hope this is useful.