I have a new bathroom in my house. The bathroom is completely roughed
in.

The subfloor of the bathroom has radiant panels---the pex is visible
and runs in grooves in cdx plywood panels that I installed.

I am planning on building a shower next, and the first thing that I
want to do is build the curb.

My thought was to build a form and pour the curb from concrete. The
curb will not be too large (the shower is in the corner of the
bathroom) and I have a few bags of concrete sitting around. I know
that some people make curbs from PT but this seems risky to me.

My question is, what do I put under the concrete curb? I need to
protect the pex. Should I put roofing paper under my concrete form?

My second question is, how best is a concrete curb anchored to a
plywood subfloor? If I were going to pour a curb on a concrete floor
I would epoxy a few bolts into the floor before pouring a curb. This
would help with anchoring. Should I did a similar thing with a
concrete curb on a plywood subfloor?

So, this makes me wonder, should I screw cement board to the entire
bathroom floor before I do anything? If I did this (leaving out for
the moment the area inside the curb, or maybe including this area)
would be curb bond to the concrete board?

Thanks,

Mike