As Rocklobster said, steel wool and elbow grease on the racks, followed by either several coats of Rust-o-leum silver spray paint, or the expense of having it re-chromed.
As for the discolored plastic interior, the fact is that plastic deteriorates, and RV appliances aren't made from quality materials (insert the word "cheap" here!) The discoloration is from aging and goes the depth of the plastic as it turns brittle. No amount of "cleaning" can change that. Only total replacement of the appliance will give you a "new, clean" look.
"Food is our common ground, a universal experience." - James Beard