Tonight I used my little 12" Di-Acro Brake to bend up the floor stiffeners. Here they are after the first bend.

...and after the two outside bends. These should do a fine job of stiffening up the floor, and the rounded ridge is nice and smooth so it won't wear through the foil wrapper of my fireproof insulation (to be trapped between the sub floor and the bottom skin. There's no way these would have turned out as nice as they did without that little brake. I'm glad I upgraded from that POS Harbor Freight brake I used to have.

This stack represents half of the required stiffeners. The other half go between the outboard floor stiffeners and the lower longerons. Since those two members are not parallel, the length of each of those stiffeners will vary somewhat. I'll work on converting the other half of the elevator skin into those stiffeners tomorrow.