It reminds me of the South African Valkiri MRL which uses a tarpaulin to look like a normal supply truck.
2010-04 Club-K Container Missile system video
2009-02 Warship Stealth
edit 2012-12-01: Comments on grognews are skeptical whether it's really an improvised MRL. Well, the photo is actually two years old (hence "captured"), and another photo shows uniformed officials inspecting it so it's not totally pulled out of someone's behind. It may still be from another region than Gaza, but I honestly don't care. It's the idea that's of interest, not the location.