JFC, man. Save up $6M like your dad and then buy an annuity and that will tell you how much you can spend every year. If you have a spouse, get it with survivorship. Problem solved. Now pay me 1% of your $6M annually.

You’ll want to double check if I am correct. Let’s say you use Schluter DITRA uncoupling membrane. I would have a 1/8 inch space between DITRA and the wall. Then I would crease a 5 inch Kerdi membrane in half and bond it to the DITRA and the wall with thin set.