The treads are taller than you!!!! No one will mess with this HUGE tank! Just replace the wooden trap door with an iron one and put stone buttons instead of wooden ones for the middle of the treads. Fill the dispensers and fire away (Fire charges are the best ammunition)! Just don't press the buttons on the stone blocks, their your motor and one touch of a button will demolish your tank (mostly in the back).
NOTE: If your schematic name is too long, this will command not work in Minecraft, as the chat will only take part of the command.
If this doesn't work, you'll need paste the schematic from a mod using the blockly block below.