A couple of days ago , I asked for advice how to trim around a bath
vent i installed. Because my siding was not flat, I followed the
instructions and cut around the whole perimeter of the vent.
It turns out Lowes had a mounting block for this purpose. Although it
was too late for me since I already cut the opening, I improvised and
used the block. I think it came out pretty good
First 2 pics are before.
Third pic is the block I got from Lowes.
4th and 5th pic is the finished product.