Sergio, nice work -- these look excellent... especially the portability of the design!
I also looked at the Billy bookcases when coming up with my Ikea bass trap design (
DIY Ultratouch Cotton Bass Traps / Broadband Absorbers) but decided to go with the IVAR system. I think your setup could be really great to line the walls of a control room with while providing a nice aesthetically pleasing and professional look (in addition to their use as a room divider trap).