I also have a long arm with a dead bar, and if the backing is pieced, I prefer to have a horizontal seam, but I can deal with vertical. wide backings are great to work with and Connecting Threads and Marshall's Dry Goods both have nice reasonably priced selections. I have done some quilts with pieced backs. My machine has no problem sewing thru the layers, but the operator had some problems getting the backing loaded on the frame perfectly straight :-). I know about the Flynn method, but haven't tried it yet.