i run a mgf restoration company and we powder coat the subframe.they are treated first the zinc plated,powdercoated then wax injected.
we also can do carbon fiber dipped things as well,i used to work on minis years ago,a true british car that no one has ever been able to copy.
i don work on minis and dont really know much about them but some of the services you guys need i can do.Always happy to help out the world best small car