This is the second configuration for supporting the floor’s wing panel (the portion between the main floor panel and the passenger-side sliding door). The previous two photos show the original wing design, which used three support posts along the wing’s outside edge. I got tired of fussing with the posts---one of them had to moved out of the way when putting Ralph Tripod under the floor or retrieving him from the same space.
Here the outside edge is supported by extensions (with elevating blocks) screwed to the underside of neighboring boards. The long 2x4 at right has a small plywood lip that contributes to the support. A later modification replaced the 2x4 and lip with another underside extension.