The slides for the drawers are mounted on plywood that runs the full depth of the cabinet; they are attached to the framing at the front and back. Some screws in the middle don't have framing members, but they are generally to pull the wall panel up to the object. In the cabinet with the drawers, the top shelf on top has 6 screws - four are attached to framing members, the two in the center are installed sufficient to pull the plywood to the shelf.
On the right hand cabinet, the standards were in the same location as where I put the new ones - there are framing members behind the plywood.
For the corner shelves in the bedroom slide - the back screw on the sides connects with the framing, where the other three seemed to get a good bite, but weren't as solid as the side corners. I'm not sure what is behind the ply, but perhaps there's another layer of thicker plywood.
Framing members can be easy to find, or very difficult. Typically I look for existing staples or I'll push on the plywood on an interior panel to see where it flexes. Sometimes tapping on the panel will reveal the framing.
From your description, it sounds like FR "improved" some areas such as the drawers under the dinette seats (convenient? yes, but not near as good a use of possible storage space) Your shelves sound like they were better constructed as well.
I started on installing two Maxx-air powered fans today too... both are in the holes and have been sealed on the roof, all that is left is to wire them and install the trim.
Oh, an I have a "behind the driver's seat" project underway too - it holds the trash can and a snack box. Pics soon!
Formerly: 2000 Four Winds 26Q/Ford, '96 Kit Sportsmaster 22' 5th wheel, '91 Sunlite truck camper, Wildernest flip-top canopy