A spray coating would be the last thing I use in a built in gutter.
TPO will work fine, I'd pull off way more then the first course of shingles though, I'd run the TPO at least 1 foot up. Water stop under and felt over to the bottom, run it though the gutter and up over the edge finish it off with a nice coping metal. Term bar would look like junk if you ask me.
Ideally wrap it in S/A Base sheet and cover in copper, solder the joints. Then step back and enjoy all the compliments on your work and not worry about it for 50 years.
TPO will work fine, I'd pull off way more then the first course of shingles though, I'd run the TPO at least 1 foot up. Water stop under and felt over to the bottom, run it though the gutter and up over the edge finish it off with a nice coping metal. Term bar would look like junk if you ask me.
Ideally wrap it in S/A Base sheet and cover in copper, solder the joints. Then step back and enjoy all the compliments on your work and not worry about it for 50 years.