Not quite so in-depth as the Archaeopter as I didn't take photos in progress.
Thought about being able to switch between transport and tank versions but as I had 2 sets I built 1 boat and 1 tank anyway.
Magnetizing main gun is pretty simple - just drill out the gun base to house a 3mm magnet at the top and a 2mm magnet at the base
Next drill out the back of the 2 gun barrels and install the magnets (check polarity! - use the method off the Archaeopter post to make life easier)
Magnets top and bottom make the attachment much more secure than magnetizing the top barrel only and stops the gun wobbling
Hope this has been of help!