Now that I have the floor rust repaired and am trying to figure out how to bend new metal to fit compound curves in the wheel wells, I suddenly find gaping cancer holes both ends of the underbody just below the taillight pockets.

I can look up through the one on the driver's side and see the taligate sill from the underside.

Also, the entire edge of the ledge that meets the top of the bumper is rusted accross its entire length.

It is all hard to get to because the holes are way up above the bumper shocks.

There is lots of surface rust, too, so I think this may have rotted from the outside - in. Is there an inside-out (downward) path?

I can't see anything from inside the cargo hold nor in the spare wheel wells to indicate such. Both cargo panel widows were leaking for who knows how long. Could they be the source? If so, where it the path the water took?

With no torch or plasma cutter available, what tool can I use to reach up there from under the bumper and cut howizontally to remove the cancer?