Hey @Amos I am going to give you two options.
Option one, The Rubbermaid Action Packer - I would call these "weather resistant" But you could water proof them but putting the things in them in a contractor grade garbage bag. These are lockable (with a padlock purchased separately) which is a feature I like.
But, I find it hard to secure hard, square boxes quickly to the basket I use. It is easy for the hard plastic to slide against the metal of the basket.
Option two, The Seal Line Black Canyon Bags - This one is 115 liters - Waterproof, durable vinyl, they are extremely easy to secure to the basket, and they are more aerodynamic - so a little less wind noise, and the bigger ones have backpack straps.
I hope those options help. Have fun out there!