I left the back of mine open too when I built it. Though the lip doesn't cover the black plastic piece completely. Just 3/4" of it (piece of quarter round and the molding to match the height of the qr). I just did it for aesthetic (sp?) reasons (and to cover up some of my ummmm.... mistakes).Valous said:no i ment is it needed to hid the trim. I can see if the tank was veiwed on all sides then yes but if the back of the tank is up against a wall then I dont see a need for the back panel at all. Atleast I have left mine open.