Here's what I do:
I take **cheap** lightweight fuseable interfacing (like what you use in clothing), and fuse the two pieces together. Sometimes I butt the edges together, sometimes they slightly overlap. This is fast, cheap, and works really, really well.
I did this on one of our charity quilts, trimmed the edge and had one of the ladies look for the overlap. She was not able to find it, even with the binding still off the quilt.