I always figure covering type weaknesses is a good first step for monotype teams. So from your list, definitely grab Drapion to block Psyshocks. Maybe even give him an Assault Vest to take the Psyshock-user's other special attacks well, I think it'd be pretty cute since he gets Knock Off and a whole slew of coverage. Plenty of ground immunities in the poison world as well, and on your list I really like Weezing, as it can spread burn through Will-O-Wisp really easily which lets the other members of your team take Earthquakes better if need be.
Oh yeah, Drapion, Scolipede, and Weezing pretty much have their spots secured on the team
I was sorta looking to try a gambler Drapion just for fun; Sniper with Night Slash and holding a Lens, so heads he does double damage and tails he does less damage than Crunch
I didn't see Knock Off in the movepool at first, that'll be great