I just installed an exterior door at the bottom of a basement
bulkhead. I framed out the opening for the door using PT 2X4s since
the boards rest (end grain down) on a concrete floor. The pre-hung
door sits on a bed of silicone caulk and I nailed it in place to the
2X4s with galvanized finish nails.

I now want to trim out the door to give it a nicer look and so that I
can insulate between the jambs and the rough opening. What is the
usual advice here? I could use PT for the trim since I will have the
same end grain problem with the trim that I had with the framing for
the rough opening. Also, the edges of the trim will be touching
concrete since the basement where the door is installed is not a
finished area. I am not sure if having wood touch concrete on an edge
is a problem.

So, I see two potential solutions. One, use PT 1X4s for the trim. I
will not have to worry about moisture from the concrete, but the idea
of PT trim seems a bit weird. Painting wet PT does not sound too
useful.

Two, use pine trim as I would for a normal interior door and keep the
bottom of the trim 1/8" off the floor. This solution is more easily
painted, which is nice, but will have pine edges touching concrete.
No end grain issues here, but are pine edges that touch concrete prone
to moisture absorption?

Any thoughts would be appreciated.

Mike