I can get you pics of mine when I go to the lake but it will be a while. On mine I just removed the doors under the tv and cut the cabinet opening out to install the mantel sides that came with my fp.
On my brothers we mounted the fp in the center under tv and used shelves removed to build in around fp.

[IMG]

http://i.imgur.com/cxTe2Q6l.jpg[/IMG]
DW had a couple of pics. First with gray frame is ours. Gray texture was what DW wanted. I included tv pic to show expanded metal I use to let heat escape from back of units.
Second was a friends I did with sheet metal fillers. can't get brothers as he is camping somewhere.