I started using that fusible tape, but I found that if the edges aren't perfectly straight I ended up with little gaps with no batting in some places. And once it's on, it's on! I don't think it's worth the cost to me to continue using it. Unless I would happen to have a show quilt someday. (!!!)
Before that I used Elmer's glue stick and stuck the pieces together. It sets up pretty fast. Yeah, there's a tiny overlappy ridge, but after the quilt is done and washed it's not bothersome to me. I've even glued multiple chunks together to make the big batting piece.
Before the glue I hand basted with big stitches.