I dug out a number of long boards from the board pile at the mill, and between Grandpa and I, managed to get them cut and positioned over the course of two days. It required a fair bit of moving back and forth with the ladders to place and then screw down the boards.
In the corners, I ran a pair of 2"x4"'s from a block on the sauna to the corner of the fascia boards of the porch. The angles were very challenging to get right, as they had to be cut in all three dimensions! I think they came out better than I expected, but as I've said before, I don't think I would go with a non-vertical fascia board on the cabin or other future porch roof.