There were a few options online, some hard cases that would provide lots of protection, but at a price that I really didn’t want to pay. Further Googling brought me to analternative: the Vincita B132B “soft transport bag”.

Vincita B050WP-A small waterproof panniers

Most people in the Philippines assume that riding around with any sort of load requires that you carry it in a bag you put on your person. The poster child for this is the backpack.