Use expensive stretch tape for the tricky parts and regular non-stretch tape for the rest
This is a hybrid approach to pan flashing from Dave Joyce and John Albert of Synergy Construction. It uses both standard non-stretch flashing tape and a stretchable tape.
It begins, as always, with a sloped sill.
Then John applies square pieces of stretchable tape to the corners.
Next, he cuts the flashing tape top length and removes one side of the release paper.
Working from his left to right, John applies the flashing tape to the sill, turning up the edges a couple of inches at each end.
Because the corner is already flashed, you can just cut straight up, allowing the bottom flap to be applied to the exterior foam when that is added later.