In the very back, the steel hold down plate should be under the plywood floor. On either side of the frame in the rear, the banana wrap covers it, then further forward your side panels actually come all the way down and form the banana wrap. If you look for my thread "Aviators 1970 restomod", I recall posting some pictures when I got to that point. In mine, I used a stainless steel hold down plate to reduce galvanic reactions.
Craig and Carol
1997 34' Excella 1000
1970 27' Overlander, International
2009 Ford F150 5.4L
ProPride hitch with 1400# bars
Past President Southeastern Camping Unit (12)