I can confirm there is a backing plate there. I added padeyes for my asymmetrical in the exact same location. There are access plates below int he aft cabins, it was still a bit of a PITA to get the washers, lock washers and nuts on dues to the small access but it's very doable. One warning: make sure you bed it in plenty of sealer to prevent leaks and tighten it thoroughly. Also, do to the area below, drill as far inboard as your padeyes allow so you have room for a good sized washer to lay flat, too far outboard and you could have the washer bind up where the fiberglass curves downward.