Don't know if you've poured a mud pan before but I've gone away from them. I'm now using preformed pans or shower pan kits. While they are more expensive, the Quick Drain kit I'm using now for a 5×5 curbless shower with a trough drain was $850, I feel my liability is way less. It installed in less than 2 hours. Quick Drain is located in Frisco has good tech support so maybe check it out as an alternative.