Don't see why not, don't think it can do any harm - the main thing is that there is as little rust under the powder coating as possible, I believe the Waxoyl will self heal over any less than perfect powder coating and offer a degree of extra protection. As mentioned on earlier posts it is very easy for rust to develop under virtually any paint etc ! Poor quality,steel made from scrap iron etc contains so many impurities it will find any moisture and rust, whatever you do ! All you can do is to help retard any moisture from both inside and outside the steel, so a little extra coating of Waxoyl shouldn't do any harm :)