Amazon offers Prime members the Rust-Oleum 18-oz. NeverWet Waterproofing Spray Kit, model no. 274232, for $10.03 with free shipping. (Non-Prime members can spend $35 or more to qualify for free shipping; otherwise, shipping adds $7.39.) That's $2 under our mention from two days ago and the lowest total price we've seen. (It's also $7 under what you'd expect to pay locally in-store.) This liquid-repelling treatment for surfaces guards against corrosion and wear. It features a low-odor 2-step process and covers 10 to 15 sq. ft.
Walmart charges the same via in-store pickup.