No backer board at Home Depot?

I'm not familiar with mounting chair rail on anything other than directly on the wall or as a cap over paneling. Do you have any pictures or links that show what you're talking about?

I can't seem to locate a good picture of it right now, but what I am talking about is a flat 5" wide board that has a bead routed along the top and bottom edge. It is probably a little thinner than 3/4" though. It's common in this area for this to be installed first and then the more decorative chair rail is installed on this backer board. In my bedrooms, the backer board is installed without any chair rail. Hope this helps.

If you want it, build it. Your choice of edge bead or mold can be nailed to MDF, which is really just a filler between the rail and the wall, to hide the build-up.

There's a big, thick, book of molding profiles at the pro desk. If it's not in the rack, it's probably in the book.

Expect to pay a "bundling" fee if you only need a few sections.

Barry

I've never seen nor heard of this either (and I thought I'd seen most of this country). May I ask what region you are in?

Eric, My experience has been that a place like The Building Center (Charlotte area) has great selection and far better pricing. TomNie

I don't use HD for trim, they are way too expensive. Their selection is extremely limited in both profiles and lengths. So I am not surprised that you were disappointed. Try a real trim mill.