We always roll a towel up and place it along the front edge of the frig. When we close the outside kitchen door, the towel is squeezed and keeps the frig. door from opening during transit.
In our old trailer the fridge latch wouldn't hold any more so I bought the 'Baby Lock' for fridges. It worked great! But it does mean that you have to stick it to the fridge on the side and front and you may not want to do that.
I put blue painters tape on mine every time we travel. It does the job. I've noticed on some new models of other brands that they have started including a velcro strap which is an excellent idea.
My first trip, I had no problems with the fridge opening, but the last trip I took the door opened both times. I think it was the way I loaded the fridge this time. I have been contemplating putting a velcro on the fridge as well.