I'd go with Mattress stitch. It will leave a seam on the inside, but will look wonderful on the outside.
There is video on mattress stitch here, but you'll pick up one stitch from each edge rather than one bar from each edge.
"Trust the pattern!"
Time flies like an arrow, but fruit flies like a banana.
Hop aboard while we follow the cloud-covered van of knitting harmony, man!! Woooo!! --Hedgehog
IngridKH on Ravelry