I sew the 2 sections together first with a BIG--prolly about an inch seam. Then I trim it off. Actually I have left on on a few times and just snipped every couple of inches if it seems puckery.
I have my own HQ16 and am a charity quilter. I stitch the seam to one side on my regular sewing machine. This makes sure it does not twist on the frame. The stitching will show on the back but that does not bother me at all. I doubt it will other the recipient either.
I am sure the quilt police would stab themselves in their eyes if they saw me do this. My goal is a very well constructed quilt that can withstand many washings and much use.
I do any trimming for my sewing on my kitchen counter which is a perfect height for me.