I use these; a bit heavy, but they stay dry inside when it rains.

https://www.homedepot.com/p/RIDGID-22-in-Pro-Tool-Box-Black-222570/205440481


@Amos wrote:

Anyone have any recommendations for weatherproof (waterproof would be better but impossible to find?) storage bins/totes? Not looking for a cargo box. Looking for smaller bins that can be strapped to the basket.

Thanks for any suggestions!