Nice idea, but let’s not jump straight into the glue‑gun. The first thing to check is the material of the panels—if you use too thin a cardboard, the glue will just spread and the panels will separate under even a light hammer. Start by mapping the load path: every joint has to transfer the full weight of the next layer. For a modular fort, make each panel double‑thick where it will be loaded, and use a high‑strength adhesive with a quick‑set cycle. I’d sketch a 2‑D grid on paper: label every stress point with a weight estimate, then run a quick pressure test in a small tower before you even think about cereal boxes. Once you have that baseline, we can tweak the glue line spacing and maybe add a metal bracket at the corners. Let’s not just snap together; let’s build a test plan first.