If you have steel walls, you can still put up a vapor barrier to keep moisture out of your basement. Steel walls require mastic and a clean surface in order to apply the waterproofing, so install the mastic and then put up the vapor barrier. You need this vapor barrier because steel walls are still effected by condensation and evaporation, which will quickly change the environment in a building. Be sure to cover the whole wall with the vapor barrier, and make sure it extends to the concrete slab.