I wish the controller weather protector came with a protector for the plug that had room enough for a surge protector. We have lost other controllers due to surges, and now have a surge protector on our power supply. Frustrating that even the smallest surge protector doesn’t fit well into the weather proof covers.
You don’t have to by the small Rachio box. You can use any kind of box you choose. This is the one that I used at my house prior to Rachio having their own many years ago. It would be plenty big for a surge protector. Sadly, they are considerably more expensive than they were 6 years ago!
This ebay seller even “brands” it for Rachio!