Ally or steel floor (and tank)?

[alga]

Hi, what are the pros & cons of the ally and steel floors? Ally is lighter, steel is cheaper? Is that it?

Due to lower electrode potential the ally floor will protect the chassis from corrosion, by oxidising itself. Somehow I doubt that dipping rivets into silicone will electrically isolate the floor from chassis. A contact will appear in one place or another.

On a related question, why is everyone so keen on fabbing the tank out of sheet ally? 1 mm mild steel sheet would be so much easier to DIY (MIG FTW!), and it would weigh only around 5 kilos. Are 2-3 kg savings worth the effort and the expense, or are there other benefits I'm missing?