So is it just lateral support that is questionable at the moment, if so I will add 2 horizontal shelves and frame the sides and top with a 4 " ply trim, this is not my first wood project. I am not a carpenter but I have built lots of structures including a 40' shop 15 years ago that is still standing today.
In my opinion plywood is extremley strong the layering in oposite directions of the veneers if built properly ,would be just as good as a plywood on frame design. cabinet makers stoped building framed cabinets years ago.
I do think I should have used glue and will take it apart and glue every joint, thanks for the input so far.