Going to be installing a shower insert and surround, my exterior wall is where the back of the shower surround and pan will be going. Behind my drywall there are just 1x4 furring strips attached to the exterior block wall. Would that be enough to screw the pan and shower surround to or should I stud it out? The current shower is an alcove that is only 32" square but it was tiled and the backer board for the tile was attached to the fur strips. Both end walls will be standard stud once I built out one end. Thanks for help