[EricH]

In my time on 330, we had some really nice plywood bottoms. 2005, we took aircraft-grade plywood, cut some pieces to match the openings in the frame that we wanted to cover, and cut a piece to match the entire bottom area to cover. Glued them all together, and had a strong belly. 2007, we looked solid from the top. The bottom of the belly pan (1/4" ply, I think) was a spiderweb of strength and thin areas. Attachment points were full thickness, supports for the attachment points were full thickness, everywhere else was thin. A skilled hand with a router was all that was needed.