PSA: skip the packing tape and use a hot glue gun on box seams, my fort survived a whole weekend
Built a two-room fort with my niece in the living room two weekends back. First attempt got wrecked by packing tape peeling off the flaps. I switched to a cheap hot glue gun on the seams and that thing held through her cousins coming over, a dog running through it, and a full Saturday of chaos. The glue actually sinks into the cardboard and makes a solid joint, while the tape just sits on top and gives up. Only downside is you need to hold each seam for about 10 seconds. What are you all using for the tricky corners where two walls meet at an angle?
Glue those corners too, it works way better than tape there. Just dab a good bead and hold it while it sets. Tricky angles are where tape always fails anyway.