I just did mine a few days ago. I installed a Pirelli MT43 and had it go flat twice in two rides. Both times the valve stem was ripped out from the tire spinning relative to the rim. I drilled my second hole close to the hole the valve stem goes through which is almost opposite the existing rim locker hole. After drilling the hole and installing new tube and MT43 I wish that I had drilled the hole 1 more spoke away from the stem hole. The way I have it, 2 spokes away, is too close to the stem hole so the rim locker pushes the valve stem a bit. I think 3 or 4 spokes away would be ideal. I was thinking putting it close minimises the movement of the tire relative to the stem.
Greg