I took the carriage bolt approach as in Figures 9 and 10, but only used three instead of four to make it a little harder for the middle grate to hang up when trying to tilt and remove past the top grate supports. I leave the carriage bolts attached to the bottom grate all the time, whether supporting a third rack or not since they don't get in the way or anything.
I just did another big 20lb leg quarter cook this evening. You might say I have to start with a little more charcoal.