I only use metal frames for my photography, so I never use the paper cover on the back. The paper is standard practice for wood frames.
For metal frames I skip the spring clips because they don't hold the mat(s), mount, and backboard tight and even to the ENTIRE surface of the glass.
What I feel works best is small strips of acid free corrugated cardboard. (It's a blue cardboard that I get from my mat board supplier). The strips fill the entire space below the frame moulding and the backer board and prevent any little bugs from sneaking in between the glass and top mat.
Another option that I have seen is taping the glass/mat&mount/backer together to form one unit. The tape seals out all moisture and prevents critters from entering. I don't do it, but have seen it done before.