You could take a slightly more offensive approach and go with SubDisable Gengar.
Gengar @ Black Sludge
Timid - Levitate
252 Speed, 252 Sp. Atk, 4 HP
Gengar helps you win stall wars by shitting on opposing stall-based Pokemon. Most stall-based Pokemon rely on passive damage to take out threats and carry only one attacking move, if any (Skarmory's Brave Bird, Ferrothorn's Gyro Ball/Power Whip, Jellicent's Scald), so you can Substitute, blocking out Will o' Wisp and the likes, then Disable their attacking move when they use it to break your sub. Set up another sub, and they're helpless as you blow them away with Shadow Ball or Focus Blast, which offers the best coverage possible, hitting everything in the game at least neutrally. On top of that, this set forces a lot of switches, racking up Hazard damage.
Now Meganium... To be honest, I'm not even sure how a cleric or Grass type benefits you much, so I'm going to recommend the king of DPPt stall, still a threat in 5th generation, TormenTran.
Heatran @ Leftovers
Calm - Flash Fire
252 HP, 252 Sp. Def, 4 Def
With 12 resistances/immunities, a LOT of threats carry only one move that can even slightly hurt Heatran, which makes Heatran one of the few viable users of the Torment stalling tactic, which combines Torment and Protect to either force switches or rack up Toxic damage. Plus, this shits on Choice locked wallbreakers as they can only hit him every other turn. Standard TormenTran runs 220 Speed EVs to outrun max Speed positive Tyranitar, but to be honest he doesn't seem to threaten you much as is so maximizing bulk will probably get you farther. It also normally runs Substitute over Toxic, but with an immunity to burns and poison and the ability to 2HKO nearly all users of Leech Seed bar things like Sp. Def Celebi, there's not a lot it does for you.