A few on this site have done it. Search the previous threads. Personally I love my open back. If you do decide to tackle the project it will require some careful cutting of the perimeter of the back wall. The edges will need to be sealed (with epoxy or polyester resin) and gelcoated or painted.
Agreed! I initially had concerns but after using it for a season I would not want a closed back. I feel disconnected enough from the back deck when the canvas is up.