Long horizontal pieces would risk stretching (at least in our experience) and causes issues matching top to bottom splits on anything longer than say 15-20'
We print vertical panels. We measure each panel. 1/2" bleeds (1" overlaps) at each vertical edge/seam. More at top and bottom and two ends.
I've seen shops assemble the whole thing, then roll it down off the top of the trailer. Crazy scary. We install each panel individually.