My son has a very small bathroom in his house. He only wants a shower stall in the bathroom. Looking at the available space and plumbing restrictions, his stall can only be apporximately 28" wide with a maximum of 48" long. The door will have to be ay an angle. My question is can a base be purchased at 28" wide or should I make the base myself. Would appreciate any help in making the base especially mortar and rubber seal ideas.