Panting in metal pots?

My plants are 3 weeks old today and I will be repotting them in FFof within the next week or 2. My gf bought a few large (2.5 or 3 gallon) metal pots for various plants around the house.
I've noticed in the past that the metal pots will rust internally. I'm wondering if it's bad for the plants/roots.
Should/could I spray the inside with rubber undercoating? I plan on putting an inch or 2 of gravel in the bottom, but what about the sides? Is it safe?

I would get other pots or at-least line them. no telling what is in the metal. (China has made radioactive cheese graters before - by using scrap from nuke plants - bad juju) http://www.dailykos.com/story/2008/09/22/596575/-Radioactive-Cheese-Graters-from-China-(not-a-joke)
so they could be radioactivity, mercury, lead, cadmium, and a host of other nasty compounds in them. since they are pots designed for planting house plants they are completely unregulated.

I have a very healthy plant growing out of an old tin minnow bucket. If I get some nice fruit off it the strain will be called "stink bait." Ya baby...