Hey, A client has asked me to do exterior casing (1×4) for their new windows.  This is new construction.  She requested no exterior sill and its being sided in clapboards.  I have done this work before yet I have questions about what to caulk and what not to caulk and why.  I flashed them well.  Mostly looking for feedback.  

I installed the casing and caulked behind it on the legs and the head but not the bottom piece.  The bottom piece is 7 inches shorter in length than the head, as per usual.   I am laying out my clapboards and will have the bottom edge of the clapboard land at the top of the head casing and again at the bottom of the bottom piece of casing.  There will be z flashing at the top of the head casing.  All good so far.

I plan on top caulking between the window frame and the casing on the sides but not at the head or the bottom.  At the head, I will not caulk between the window frame and the casing (where the factory watershedding lip is) so that water can escape .  I will do small caulk dams at the ends of this factory piece to prevent water from running down the sides.

At the bottom, I will not top caulk between the window frame and the casing, nor will I caulk between the casing and the sheathing (no rainscreen).  This is where I get nervous.  With no sill and no kerf, the water runs down the face of the bottom piece of casing, wicks back toward the sheathing and stands a good chance, in my opinion, of getting behind the clapboard.  I am considering doing a caulk line behind the clapboard but I dont want to create a dam that might prevent water that had gotten into the window from escaping. 

I am realizing that I should have advocated for sills.

Any advice?

thanks,  Stephen