You have choices for mounting flatscreens in place of CRT's......
If you are ok with a smaller screen, try to find a flatscreen in the width that will fit right behind the framing of the opening. Then just fashion some brackets to hold it in place.
I wanted something a bit larger, so I used a 1 x 12 mounted across the opening, then mounted a flatscreen right to that board, using a fixed TV mount. It sticks out an inch or two, but is mounted solidly and looks good.
Paul & Sandra
Plymouth, MA
2014 Heartland Cyclone 4100 King