How to combine multiples colliders

Hello,

I’m trying to create a blueprint actor consisting of a billboard following player’s location on the closest point of a “big collider” composed of multiple overlapping box collisions, added by hand on an instance of this blueprint.
With a single box collision it works like a charm thanks to the node “Get closest point on location”, targetting a Box Collider.
But what i’d like to do is to be able to merge several box collision that would act like one, more complex collider and the billboard moving on the surface of this big general collider.

How could I merge several box collider into one ?
On the picture, the red line shows the billboard movement along the “big complex collider”

Volumetric_billboard

Thank you