Don't just close off the vents but insulate. Since the residential fridge will need airflow around it, the vent and lack of insulation would let a lot of cold air into the RV. Lots of folks over on another forum where I'm a moderator have done the conversion and are very happy with it. Be sure to research the reliability and customer ratings on the new fridge you are considering.
Sorry about your health issues.
Rob
PS: we have a factory-installed residential fridge and have experienced temps in the teens without any issues at all.
