Do you want to grow the box while maintaining a fixed orientation? If so, you can just transform the plane vertices into the box’s coordinate system. The box is axis-aligned in its own coordinate system so you can treat it like an AABB and just take min/max of everything.

For my airplane game, my drones are shooting some magical boxed towards the enemy planes. The boxes rotates in all directions as they approach an airplane. Once it hit an airplane, it should resize itself so the airplane fit inside the box and is them trapped. The problem is, the box is not axis aligned. Is there an algo somewhere that allow to fit a set of triangles in it and the box grows as you add triangles in it? like AABB does?