If you take the Duke in a list that also contains warriors or trueborn, he has to start in one of those units, and neither of the venom squads have room for another model in their boats. I'd recommend putting in a nine-man warrior squad in a raider with splinter racks and night shields to take best advantage of the Serpent's Venom. In fact, Night Shields are useful for any shooting unit. At a thousand points, you may as well drop the Razorwing to help make room, and the Grisly Trophies on the Wych raider are also unnecessary. The wych unit itself looks decent, though.