I personally don't think you should pick Scolipede or Toxicroak. Toxicroak can be good when used with a rainy strategy but unless you know you can set him up with that then I wouldn't go for it. Giving him Rain Dance isn't any good either because he's not really likely to survive long enough. Scolipede, in my opinion, is generally bad.
If I was putting together a Poison team, I'd go for Gengar, Drapion, Venusaur, Venomoth, Crobat and Tentacruel, but that's just me. Tentacruel does well as a Special defensive with Barrier, provided you can ensure he doesn't get hit by too many physical moves. Venusaur, obviously, is generally good. Venomoth can run Quiver Dance, which again has a risk of physical weakness, but I think it's worth it as long as you can back some of your other more Defensive Pokémon up with some extra Def EVs or Defense increasing for the situation. Crobat isn't as good as it seems, but I do think he has potential with Acrobatics and Flight Gem, along with some other stuff you could throw in there.