Obviously there's no LATCH system on a 123. So I'm wondering if any wagon owners have added a top tether attachment, and if so, where?

It seems that the best spot would be between the strip of floor between the rear seat and storage door, which runs the width of the cargo area and maybe 6 inches wide. My wagon does not have the 3rd row seat. I noticed last night that there are a few screws holding down that piece of interior flooring.

Any input would be greatly appreciated. I'm sure that the normal shoulder/lap belt will work fine, but as springy as those rear seats are, I think a top tether would add some stability.

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1982 240 D, 308,000 - 321,127 miles (sold)
1982 300 TD,166,500 - 226,000 miles
1998 E 320, 120,000 - 144,000 miles
2005 C 230 K, 26,000 - 77,000 miles (sold)