You're out of warranty, but don't fret, Isuzu of America rarely honors their warranties anyways.

The chrome peeling on the wheels is common, some owners have actually gotten them replaced, but this was when the vehicles were only a couple of years old.

Good news is, it's not rust. The wheels are aluminum. You are just seeing the oxidation from the raw aluminum coming in contact with air.
Bad news is, it's impossible to fix with just a coating. Those rust stoppers convert iron oxide. This is not iron.
The only way to "fix" it, is to have the wheels stripped (an expensive and hazardous process, due to the chemicals involved) and either rechromed or anodized (which would be great).