Here is the plan.  I’m in northern Utah – very dry.

The monolithic liquid exterior WRB is prosoco, and the roughs are sealed with their fast flash. 

Andersen 100’s can be installed (method 2) by sealing the entire nail flange, with no water gap at the bottom.  The Andersen rep said he was perfectly ok with sealing the entire flange considering the prosoco flashing of the window.

Loctite window and door foam to seal.  

Logic – > If there happens to be a window failure, I want to know over the next 10 years so they can replace the window. Therefore let the water that happens to leak through cause a small problem.  In Utah, water leakage doesn’t mean rot.

The air tightness and insulation value of loctite will be superior to backer rod/sealant.