Can't believe a manufacturer can get away with such poor design, I think the only way is to get the biggest backing plate under the deck and bolt through into it. The Inspection hatches sound like a good idea but will limit your backing plate to 4 inches in one direction, they are available in 6 inch which would be better, as would getting the nuts welded onto the backing plate to save hassle when fitting. It may also be worth cutting the ends off the A-frame and getting them welded back on at the right angle.
The wooden blocks are probably what caused the failure. They most likely soaked up water got soft and allowed an amount of movement that gradualy weakened the mounts.
If you need any help just shout.
By the way, I promise I'll get those kids life jackets back to you very soon.
RIBBED For extra pleasure.
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