I have for you an excellent brine for white springs I got off a chef I met on the flow. I smoke my salmon with a variety of different recipes, last year I tried this one and everyone who tried it said it was their favorite out of the 5 kinds I had (better than red spring coho, chum et al). It is a very simple brine but I highly reccommend you give it a try. Cut the Spring into fairly even strips. You can do singles, doubles or triples. In a non-metallic container place one layer of strips down leaving space in between them for the dry brine. Lightly sprinkle the fish with brining salt, then hard pack heavily with brown sugar. You want the fish to be completely covered in brown sugar with the spaces in between filled and with no fish showing on top. Repeat with additional layers if needed. I don't remember exactly how much brown sugar I used last time but the above is how the recipe was explained to me and it came out great. For a 30lb fish you will probably need 2-3 bags. Let brine covered in the fridge for at least 48 hours. Once the brine is mostly liquified (after the first 12hrs or so) move the pieces around a few times to make sure they are evenly brined and also to move the salt around in the mixture. If the fish is floating up and protruding out of the brine you can weigh it down with something (non-metallic). When ready to smoke place the fish directly in the smoker do not rinse the strips. Place the thickest strips on the bottom rack. Smoke heavily with alder chips (or alternate with a couple pans of cherry for something different) for 6-8 hrs in a Big chief smoker (Times will vary depending on outside temp or if using another smoker such as Bradley with a heat control.) For the first 4-5 hours you want to change the chips frequently; immediately once they blacken through, approx. every ~40 min. Dispose of the last pan of chips then cook the rest of the way adding 1-2 or so more pans infrequently. I have found when cooking in cold temps it is sometimes necessary to baste the fish with honey with a very small amount of water if you find the outside is drying out and and appears to be getting overdone while the inside is still mushy. When smoking the fish you want to keep the door shut as much as possible. I would recommend waiting until the 6hr mark before checking it and be fast when you do so. The finished product will be black in appearance but will not taste burnt it will be very tasty.