[DanielDudley]

I use the leveling compound from HD as well, it is great stuff. I would glue and screw backer board down first, and use the primer on that. If I need to, I put a reference line or small nails in the wall to float up to. I feel more comfortable running leveling compound on the backer board if I am leveling out to a fairly thin edge on plywood. Guys will tile plywood, but I have never been comfortable with it. You need the float with the handle. Don't do this on your knees, unless it is a really small space.

This is the stuff we use to float over electric radiant grids, and you could make a pool table out of it. BTW, if there are any small holes or gaps at the edge of the wall, this stuff will run right out. Tape them all up. I like the Custom Building Products brand. Not fond of Quickcrete products at all.