@bslon Are your two rows of Kallax cubes reinforced too?
No, but some kind of backing will keep the LPs from sliding in too far in as the backs are open. I taped down cord hider to remedy that.
Horizontally, they’re very sturdy. I wouldn’t run them very high if used vertically. The interior dividers are held in place with 4 dowels, I’m not sure how they’d handle the weight of LPs if they were used as shelves.

