My 2 cents, after doing a fair number of quarters:
1) Wet brine for at least 6 hours prior to smoking. You can add flavorings to the brine like pepper and garlic, but you should rinse the quarters off before putting them on the smoker, so much of the additions to the salt brine will be wasted.
2) smoke hot-n-fast
3) finish them on a grill over open flame if you can to crisp the skin
4) as one of the links above advised, sauce at the end, not during the cook. This of course wont matter if you want to crisp the skin like in number 3
5) get them off as soon as they are at the minimum IT, since they will continue to cook and dry out
Hope this helps
