The regular Schluter pan has a lot of slope in it. I was curious and put a 4' level on mine. Once the walls are covered, corners are in , all joints sealed , kinda reminded me of it being fiber glassed . Looks like it would be sealed mighty tight. That custom made one is a good idea but fit could be iffy and no telling the lead time and cost of just the pan. That Schluter stuff is high enough.

Been wondering why there isn't a system out there similar to Schluter where last thing you do is spray it with something like Rino Lining.