My advice would be not to build a media wall in the first place.
What happens in a few years time when you want a larger screen for instance ? You going to rip it all out and start again ?
Media walls are really a product of the 1960's/70's, when tv's were small in screen size but massive in bulk.
My 77 inch G2 is not even 30mm in thickness, why the hell would you want to bury it in a media wall ?