A few years ago, I added a 6x8 closed-in porch on the southeast corner of my house. I left the original outside wall with cedar siding alone [inside]. I drywalled the other three walls. My question is...what kind of insulation or filler can I put on the inside corner of the south wall. Because of weather changes. It cracks and opens up. Pollyfill does not work. Could I use a spray foam, or a flexible silicone caulking???