Add center cushion to front seating older boat

The newer boats have the center cushion (circles I’m attached pic). My older tige does not have the center cushion. Anyone have pictures or able to take pictures of how the center cushion is installed? Does it rest on the fiberglass that the main front seats rest on? Is there a support screwed to the fiberglass area to support the center cushion? I’m redoing my upholstery and want to add this center cushion and if I need to make front seats a little more narrow or add supports, now is the time for me to do it.

Thanks