I'd tell you but I'm too jealous of you owning a volcano so I can't reveal that info. :thefinger:
Basing it off of what I've seen, I've seen NOS Benelli Volcano fuel tank straps made out of plastic show up on ebay in years past. So they must have some sort of strap to hold down the tank that snaps together. I seem to recall the Volcano also having cushions the tank sits on (like a Honda z50).
And if you ever want to sell that bike..PM me!!