Tile Countertop Support???
Use backerboard but FIRST, level the counter with Leveler. THen, you won't have the 'waving' problems you're talking about. It's OK for the counter to tilt VERY slightly to the rear. If yours does this, just make sure your backsplash is a GOOD one. (You don't want dishwater or any spills ending up BEHIND your counters ...)
My best to ya and hope this helps.
Jay J -Moderator
PS: God Bless America!