kr on older coachs the vent flap was on the outside wall on later coachs they put vent thru roof with cap. Your signature info is not posted so I will say you may have a kitchen slide. The older vent flaps had a tab that would close and hold flap from flapping.
You need some kind of tab from hardware store with stainless steel screw to hold tab to lock flap closed. You can use as I did your awning rod to close tab over door flap.
With your vent sealed as it is your going now have all moist air and cooking oils blown back into coach, not a good thing.
Information on your coach can be filled in your signature block on second page of your profile it will be just below where I have added your KARMA as member of this forum.

Did you find paint code for painting your HW heater door. Sherwin Williams should have spray cans to match your paint for door.