GOAN, have you ever seen a svara for why it was covered in baatz?
(I always thought that it was because of rust, and maybe that tin rusts more slowly that iron (though it does rust as well), but lfi this Rogachover they didn’t use it for more than one day anyway)
Also, the lashon of the gemara about their monetary status is a bit funny if it is talking about tumah, as it only should have been for those 8 days (although his pshat can just be an added benefit to using the shpudim).