Like my own quilt backs, I prefer customers' quilt backs to have 1/2" seams and with the seams pressed open. No 1/4" seams please...too big of a chance it'll pull apart if topper accidentally uses a 'scant' on the 1/4" seam. Pay attention to your stitch length (not too long...not too short) and stitch tension (not too tight...not too loose)!
Here's a back I made and longarm quilted without any problems. The front was a '1600 Quilt' (leftovers used on the back) - lots of seams - no problems at all with the multiple seams on the front AND back!
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Final thought...ask your longarmer what they can do or what they accept for backing material.
Have a wonderful weekend!
Nancy