Boxes should always be taped and not folded.
Run 3 pieces of packing tape in the same direction as the join of the flaps on the bottom of the box.
One in the middle where the flaps meet and one either side of the join in the middle of the flap.
This will ensure good support for the bottom of the box. NEVER cross the flaps on the bottom of the box.
On the top of the box fold the flaps together and put one piece of tape along the join where the flaps meet.