I don't buy the riffability of a movie that's INTENTIONALLY a joke. I mean, come on.
Silent Rage, among others, proved that poorly conceived and executed humor is completely riffable. The "frozen dog" story was supposed to be funny. Wow, but it wasn't. The guys found riff fodder, though.
I don't think the guys would make a live show out of Sharknado if they couldn't do a good job of it.