Another porch question for you all!

Our porch is going to have a Hip roof. To maintain as much ceiling height as possible, we’re looking to match the contour of the Hip and keep the ceiling vaulted.

I’m thinking keeping the joints tight enough will be damn near impossible (using a PVC beadboard product...). Any thoughts on what kind of trim I could use to cover the joints? Or is there another technique that I’m missing here?