I'm willing to bet that if you were to properly clean up that area, you'll find several holes coming through. It's not a bad area to fix though, since no real teardown of the cab is required to gain access. That part of the truck always takes a beating because anything from the front tire gets blasted up against the bottom of the floorpan.
I've also had good luck with a rust converter called "Corroseal". I'm not sure if it's available stateside, but I can get it up here in canada. And unlike Phosphoric Acid based products, no rinsing is required afterward, so you don't need to worry about it eating the metal after removing the rust.
If a proper repair is not possible in the near future, you can always spray down the rusty areas with fluidfilm. I've been using it on all the vehicles in my family and never had a lower door rust out. And since it doesn't evaporate like many petroleum products, it stays put almost like low viscosity wax. I use it to protect all the pinch welds and seam joints for my vehicles (wheel arches, floor joints, cab mounts, etc.) Just don't do it on an area that you plan to paint anytime soon.
Good luck with whatever you decide. If you were closer, I could patch that floor in a couple hours.
