I'm getting a 32" tub with shower surround that's meant for stud walls. If your alcove is deeper than the tub/surround, what do you typically cover the remaining portion in front of the apron with?

I'm looking at sheets of acrylic or plastic maybe over drywall since I have no interest in doing tile. I'd assume there's no trouble finding something like that at a big box. My real question is how to finish the edges at the corner where it will meet with drywall on the perpendicular wall? I'd also put the same material above the surround so the wall doesn't get damaged from excess spray.

Thoughts or other things I should consider?