And even if you plan on painting your hull, having the stitch holes consistently spaced will keep assembly easier and prevent from having too many stitch holes (they have to be filled in) or not enough stitch holes.
So here's one trick to keep your holes evenly spaced.
Start by making a drill jig. Space the holes in the jig according to what your build plans call for. Drill the holes just big enough to fit the stitch materials through. Make the jig wide enough so the outside of the drilled holes is 1/4" (6mm) away from the edge of the jig.
Examples:
Place the jig against the edge of the panel. We choose the spacing in this example to fit over the wooden butt blocks. Drill the hole.
Place a pin (drill bit, screw driver, etc,) into the drilled hole through the jig. Drill the second hole.
Remove the pin from the first hole and place it in the second hole. Rotate the jig around.
Align the edge of the jig to the edge of the panel, and repeat the process. Keep going until your done!