I have bought a used electrical enclosure but it didn't come with a mounting plate. Searching around it looks like they are usually made of steel but is there any reason I shouldn't fabricate an aluminium plate?

Does it need to be conductive in order to provide a common ground or is it just the case that steel is used (rather than say acrylic or phenolic etc) in case of a fire within the cabinet?

Thanks,
The Cap'n