You know there is a special parameter tag you can put on armor (FDR) and set the percentage. I have a script that does sort of the same thing based on variables. Also plays sound effects for the damage tiles and has full customization of screen flash color and multiple damage floors (you know Dragon Quest has multiple types like the marsh, lava, electric floors etc). It allows the same types of customization for poison state.
http://www.rpgmakervxace.net/topic/30961-multiple-damage-tiles-and-slip-damage-eye-candy/
I made this specifically for a Dragon Quest fan game so it's pretty much exactly the same as the original.