Hole location for Herbie for overflow's

[Delphinus]

I just make sure I have enough space that the bulkhead rim has enough of a gap around it and won't interfere with the stand underneath.

If you think about it, drilling near the edge is probably better than further away from the edge since the flex is minimized due to the edge being braced so to speak (by the seam of the vertical wall). I'd be more worried about holes in the middle of nowhere.

Only thing about drilling a 30g tank: make sure the panel you're going to drill isn't tempered (do you have polarized sunglasses? that's a good way to tell usually if there isn't a sticker) and don't overtighten the bulkheads: I've busted many smaller tanks (1/4" or 5mm glass) by tightening "one more quarter turn ought to do it".