I made a similar step on a Jeep, I replaced the plastic steps with aluminum diamond plate. What I did was drill out some holes in the top of the stainless bar and put some nutserts in the top of the bar and used bevel head screws to hold the aluminum to the stainless. then the screws dont stick up and they blend in with the aluminum. just an idea... I work with stepbars on a daily basis and the only way to keep them from rotting is to keep them clean