I'm going to insulate my 1/2" cpvc in my basement. I'm using this balck rubberized foam (like armaflex). Problem is that it is not pre slit. What is the best way to slit it to get a straight line and then seal it? I thought about laying it on the floor and laying a 2x4 edge along the center line and cutting along the 2x4, then taping it with black electrical tape on the ends and in the middle. Thoughts?