Look for either knauf RS45 RS60 or RS100 in 2" or 4" thick slabs...........either triangles called superchunks or you can straddle a corner with a full slab leaving a gap into the corner.......either way makes for a good corner bass trap.
If your treating first and second reflections in a dedicated room its pretty effective to use the knauf rs45/60 at 2" thick with a 2" gap between the treatment and the wall surface................Good luck!