I was looking at metals depot and found

P5316 3/16 (.1875) thick T304 Stainless Steel Plate - Mill Finish 1 X 2 Ft. 1 In Stock $147.52 $147.52

or

S411 11 GA. (1/8) thick T304 Stainless Steel Sheet - Dull Mill Finish 1 X 2 Ft. 1 In Stock $84.98 $84.98

I am thinking Aluminum diamond plate...

P414 .250 (1/4) thick 3003 Aluminum Diamond Plate - Highly Polished 1 X 2 Ft. 1 In Stock $44.40 $44.40

as long as you do something to prevent galvanic action, you would be golden.. 1/4" is pretty beefy compared to plastic