Uberbi.. nah, I can't do it.
Does the underlayment go perpendicular to the subfloor? And do you mesh tape the joints? I'm using a shower pan. Underlayment below the shower pan as well? I'm not sure the rough plumbing is high enough if I need to put the backer underneath the pan. If not, what would raising the rough plumbing 1/2" entail?