we had a similar situation with a previous trailer, not the vents but the space above the fridge. the fridge "cabinet" was sized for a larger 2 door fridge but a smaller single door fridge was used. there was a 10 or 12 inch high space above the fridge unused and open to the "chimney" area.
i opened it up on the inside of the trailer and installed a box to close it in from the outside and added a cabinet door. bonus storage space!!
a side effect of this was a better running fridge!
our fridges are meant to be installed in a closed space with almost zero clearance except for the back which is technically "outside". the "chimney area is supposed to sealed from the rv living area