Nick, Would painters tape, or duct tape - applied to the WSM then marked with the sharpie keep the drill from slipping?
Perhaps, though at the pressure you've gotta put on the metal when drilling, I'm not sure if it would do a whole lot for you. Even taking a nail or center punch or something that can dimple or mark the middle of the hole just a little bit, while help a lot. Just take it slow and make your pilot hole with one of your smallest bits.
Slipping is the reason you should wait before marking the rest of the holes. You're much more likely to screw something up the first time you try it, versus subsequent attempts.
I believe on my 22's install of the hinge, I slipped sideways by about 1/16". That would've likely caused an issue if I had drilled all holes at once. I basically stepped my way through each hole, drilling and installing each bolt, til all holes were complete. Takes a while as you gotta unscrew/remove the hinge each time you drill a new hole, but it's worth it ---- we're talking a $400 screwup potentially.
And finally, I'm a bit OCD, so when they say measure twice, cut once, I did more like measure 15x, cut once. I spent a lot of time carefully getting the hinge and lid centered with respect to the front door, etc. I'm a symmetry person for sure, and I of course somehow still managed to get it mounted slightly off center. The lid is the toughest part because the hinge has some lateral play, so you can drive yourself nuts trying to decide where exactly you call "centered".
