Composite box XL 300mm wide

Although 300mm on a large bed is great, could it be accommodated on an Ender 3 size bed.

Use Case

Rulebooks being stored in a cage will get damaged especially softbooks (a lot of mine are)

Potential solutions

Single box used as a base connected via dogleg brackets.

Vertical storage of rulebook in a box but the 300mm side is horizontal (if not going square, my rulebooks are c 280x210mm) with the 210 side vertical, thus protecting the pages as the book would rest on the spine.

Neither are as elegant as a full xl suite of boxi but potentially easier to