I know there are lots of straps available, cam lock straps were my first choice, but I wanted a more permanent setup for the ARB fridge as it was only going to be in one vehicle. I had thought a long time about straps and even about a slide setup. That did not work with the plan of creating a sleeping platform in the back.
I removed the rubber 'feet' from the bottom and used the bolts to screw an 1 1/2 inch aluminum 'C' channel to the bottom and then used the bolts from the center second row LR seat to fasten the fridge to the floor. It has not moved in 5 years and the 'C' channel lift leaves plenty of room under the fridge to slide a pan under it in the event there is liquid in the bottom of the fridge that needs to be drained. This arrangement allows the access to the fridge from either rear passenger doors or the front seats to access a cold drink while traveling and not having to stop, perhaps in the rain, for getting to the fridge from the rear door.