Boone,
RE: keep alive more than 10 minutes. Alewives are not hardy at all. As they prefer the cooler water, they shock up and die easier in warmer shallow water when on a hook. Some will stay alive longer, just nothing near as long as a shiner. Things that can help. Use as small a hook as you can to get by. If I want to fish at 40 feet, I hold the hook, and run out 40 foot of line, then attach the bait and get it down quick!. Alewives work pretty good for bottom fishing, as they tend to swim up and so stay in the strike zone off the bottom. I use them on downpoles, because I can get them down fast to cool water, and because its easier to check a bait on a down pole then on a planer board.

Go to 70-100 foot of water, light goes in the water, wait till you see activity on fish finder or at the light. Kill the light, then immediately throw the cast net, and let it sink to full 30,40, 50, or even 60 foot depth. As Pete said, may have to extend the handline on the cast net. Hope this helps.