I installed a 3 piece fiberglass shower. The back is against an existing wall, and I built the side walls around it. The wall with fixtures is a full wall and very solid. The other wall only goes to the top of the shower and isn’t as sturdy as I would like. Should I bring the other wall to the ceiling also, or is there a way to make it more sturdy? I really don’t like this shower unit. I wish I would have bought a base and used cement board.