@Snivy: I main a Rain Team for VGC, and thats usually what I use to battle (and my war team), so if you'd like some help, I'm more than willing to share my experiences with the team.
Also, that DAMN Gastrodon does a wonderful job walling Rain Teams, and If you switch it into a ****ing water attack, it gets it damn SpA boost. XD BUT Gastrodon can be muscled around, if fought against properly, your opponent can take it down. It seems the best type of team that would fit those three (IMO) might be an Entry Hazard Team. O3o