If the BP already contains all the meshes you would need to add a HISM component, then add an instance for each static mesh component you have, and destroy them as you go.
It would make much more sense to construct the whole thing ‘procedurally’. So, rather than stacking lots of mesh components inside the blueprint, you use the construction script to add them as instances to the HISM ( it will be the only component to start with ).
This demo uses the right concept, but you would need to adjust it to your needs
