Back in my Trailer days.. I had a "Dorm" size fridge and just put a cargo strap around it.. When I got the Class A I sold it to another camper.
They make a assorted lock systems that will work nicely, even an old fashion hasp lock like you'd use to padlock a shed can be used. Some of 'em even have a hine so you mound the fixed part of the flipper on the side. and it then extends out to where it needs to fold to go over the hasp so you can put a snap lock or hairpin (Clutch pin) in it. to lock. then when you want to get in the fridge it folds flat against he wall out of the way (one hopes).