This is a common issue among Casita owners. The Dometic vent covers for the refrigerator are held in place by flimsy plastic tabs. They can come lose or break, especially if you drive on rough roads. You might find that you arrive at your destination with a vent cover missing entirely.
This happened to us and we wanted to let you know how you can get a replacement.
Casita sells the cover through their store here: https://store.casitatraveltrailers.com/collections/vent-covers/products/upper-vents-polar-white-for-rm2454-name-price
You can also purchase the Dometic 3109492.003 Vent Cover from Amazon, which is what we did.
If you buy it from Amazon, you'll get the outer frame (in addition to the vent cover itself). You only need the vent cover and can discard the frame.
Replacing it is easy: you just pop the new vent cover in and twist the black tabs to secure it.
Many Casita owners recommend upgrading the fasteners to avoid this issue happening again. We haven't done that yet, but will report back when we do.