A TV built into the dashboard doesn't leave a lot of room for a big screen. You might start looking elsewhere in the front of the RV to relocate a bigger TV. If there's a cabinet or a space for a cabinet across from the sofa you could build a flat screen that rises out of the cabinet. If there's a place to hang it on the wall or rise up behind the sofa. The space the old TV was in would make a nice bookshelf or cabinet for travel and navigation aides. Many folks have posted pictures and descriptions of their improvements, try using the Google search box at the top of the page to look for ideas.
Bob & Donna
'98 Gulf Stream Sun Voyager DP being pushed by a '00 Beetle TDI