box construction advice needed

[myxpykalix]

I'm making a horse feed storage bin and i needed some advice. It is 6'8" long X4' tall in back to 3' tall in front with a 10" shelf on top and a 14" reveal where the lid will go to scoop out feed.

I will have dividers between sections that will act as support for the top (10" shelf). I intended to pockethole screw the dividers so they can be moved in the future, if feed quantities change.

I'm thinking i need to make a frame under the lid (where the yellow line is) to support the lid and give it a flat surface to lay to keep pests out. Is that needed? Any other advice?
Forgive the shaky lines...shaky hands...

[Tim Lucas]

I would add a face frame on top to support the lids and pocket hole the sides and partitions to attach. Then if you move the partitions you can make a new frame and it would look like a brand new box. Also it would give better support for hinging the lids and keep the mice out.