For preservation of ferrous metals, I've long used a product called "Eezox" which is comprised of a solvent/carrier with cleaning properties, dissolved in which there is a surface protectant, left behind when the solvent evaporates. I use it on firearms, swords and knives of various types. If the object is to be stored, I give it a light coat of Renaissance Wax, which serves to seal against moisture even more.
I have not used Eezox on keris, as I'm not sure of its effect on surfaces layered in differing metals. Nor does Ren Wax seem appropriate on keris, given the occasional roughened surfaces.
Someone did extensive anti-corrosion testing, using 46 different products. The results were interesting, though the testing environment is not one I'd imagine any of my objects being exposed to:
https://dayattherange.com/?page_id=3667