We have a home that has a cedar walled shower/sauna. We use this shower often as just a typical shower. Several months ago we noticed that the drywall on the outside of this shower was getting damp/moldy. We cleaned everything off and sealed the cracks between the boards inside the shower with a bead of silicone sealant. This worked… OK… for a little while, but soon the silicone peeled off and the leaking resumed. At this stage, we need to pull the drywall off and insulation out of the wall outside the shower and re-drywall. While we have it open, and the BACK side of the cedar boards are visible, what would you suggest we use to seal it from that side? What about that flex-seal stuff you see on TV?