Not sure it will work around the sending unit but they make a kit (try autozone) that is epoxy and fiberglass mat. Wire brush the rust away, goop the epoxy on the area, lay the mat down and goop some more on top. My front tank was too far gone so I bought a new one (cant remember the company name) and it came with an oring and that metal twist lock piece. paid around 170 dollars(s&h incl) and it was shipped to my front porch
They also make an epoxy stick for gas tanks. it comes in a little stick and you cut a piece off, knead it to mix it and press on the spot.
IIHO the fiberglass method works best though the stick might be better on a more precision area- easier to mold and i think you can sand it down.
