What do you mean by insulation board ? I used Celotex also called soundboard. The paper fiber board, not foam. This is how I covered the seams. I had some old white cotton bed sheets, cut into 3 inch wide strips. Mixed white glue and water, brushed glue mix over the seam, soak the cotton strips in the glue mix. Then carefully spread the strips over the seam, careful not to get wrinkles or bubbles, brush on some more glue mix, let dry. Then paint with earth color brown. The seams are hard to see. After adding ground cover they are totally gone.
Steve
