If it wasn't for my being able to reach it from the top through the open sun roof I don't think I could have gotten the housing down. It has several tabs that snap locked all around the perimeter of it. Even having access to pry the tabs back enough from the back side and release it there were 2 in the front that were a major PITA to release.
Once I had it all down I saw no benefit and snapped it back in place and proceeded to insulate the back side through the sunroof.
Good luck w/Yours