Mad science knows no limitations. There are no constraints, rules, regulations, considerations, or any of that other namby-pamby stuff regular people worry about incessantly.
You're making science here!
Instead of worrying about oxidation, may I suggest that the metal actually be radioactive? Why? For science. To find out if it could be done, and if it can't because physics itself disallows it (really, the only authority you obey, and then only begrudgingly) then to see what happens when it fails.
Villagers and their pitchforks are irritating, and I too wish there were a more lasting solution to the problem. While I can't solve that for you, I can tell you that they're going to fear, even be awestruck, by your radioactively-glowing metal-plated abomination. Other villagers in other remote mountainous lairs will always be a problem, but these villagers will get what's coming to them. Either today when their faces start melting, or tomorrow when they are plagued by horrible leukemias and cancers.
Additionally, it may even be the case that this Frankensteinian monster develops superpowers that are unrelated to, and unexplained by either his status as a reanimated composite corpse or the depleted uranium body armor you've bolted to his bones. B movie logic, what can you do? Telekinesis, the ability to breathe underwater, possibly even the ability to shoot laser blasts from his nostrils.
Finally, you do need to decide on a goal. The less utility Abominoid 9000 has in accomplishing this goal, the more in character you'll be. Perhaps you intend to drain the Mediterranean. Or colonize Venus with a slave army of uplifted wombats. How does having a Frankenstein monster help you do these things, you ask?
Seriously, what are you some sort of amateur. Don't ask questions like that, they are beneath us. Like bioethics, or hair care. You need to start thinking like a true mad scientist, and focus your attention on what matters. It can be as simple as world domination, or something so lunatic that it can't be put into words. Summoning eldritch beings from another dimension, upgrading humanity to a more perfect species incapable of emotion or free will, even just getting vengeance on those who have wronged or slandered you in the past. Only you can figure out the actual reason (or maybe you can't figure it out... just identify it).
Do it for science. Mad science.