The under-deck portion of the aft lowers is very important! I
replaced all the standing rigging at one point but neglected (forgot)
the below-deck section of wire. It failed on a windy day, and I was
very lucky not to blow a hole in the deck and/or lose the rig.
I have replaced the below-deck section with 1/4" kevlar. This is
easy, inexpensive, and longer-lasting than steel wire.
The 1/4" kevlar has eye-splices at each end, is doubled over for
twice the strength (much stronger than the fasteners, aft lowers
themselves, etc), and tightened with spectra lashing. I had one
person stand on the deck when I tightened them--they've probably
settled in a bit since then.
I have back-to-back folding pad-eyes mounted on the deck (one above
deck for the aft lower to connect to; one below deck for the kevlar
support). There is an eye-strap attached to the seatback support,
spreading the load across two 10-24 bolts.
I've posted a photo of this arrangement in the "Deck & Rigging
Photos" photo album (currently the last picture in the album).
Single-strand eye-splices like this are easy and fun, or your local
rigger can easily whip one of these up for you.
--brendan