I buy quite a bit of aluminum and stainless sheets for work at
www.alro.com they do not have prices on their website, but offer different sizes, thickness and grades as well as finishes. Sheets can be ordered cut to size. They are in several states now, but sure there is a steel supplier or 2 in every state.They make a tread plate that holds up well. Owned a Bluebird Wanderlodge before and the entire roof was done in tread plate. 3003 tread plate resists corrosion. Got me thinking how nice that would be on the bottom of my Montana....