Make the brine first. Combine the 1-1/2 quarts of water, salt, brown sugar, roasted cumin seeds and crushed red pepper in a 3-quart saucepan over medium heat. Cook to dissolve the salt and sugar. Remove from heat and set aside to cool. Place the pork loin in a large, non-metal storage container with lid. Pour the cooled brine over the pork and add the 4-1/2 quarts of ice water to completely submerge the pork. Brine overnight, refrigerated. (If your refrigerator is not large enough to hold the container, then put it in an ice chest, surrounded by ice.) Drain the meat, and pat it dry using absorbent paper towels.
Build a fire in your smoker and let it cook down to medium heat. Combine olive oil with the East Texas Rib Rub to make a spreadable paste. Rub the mixture all over the pork loin, then place the meat in the smoker. Cook until the internal temperature of the pork reads 145 degrees on an instant-read thermometer, about 1-1/2 hours. During the last 30 minutes of cooking time, begin to baste the roast with the Peach-Pecan Bar-B-Que Sauce. Baste every 10 minutes, turning the roast each time.