Depends on what you have now. If you have a Norcold 4 door fridge (1200LRIM or similar) there are several residential units that will generally fit the opening with little modification. Many times the height is more of an issue than width.
The Samsung RF197 is a popular model used by many folks. I used a top freezer Frigidaire on a previous coach. Measure your opening and head to Lowe's with a tape measurer and see what fits. Once you go residential, you will never want to go back to an absorption RV fried. Cold beer and hard ice cream is great!