Based on what I can see the entire refrigeration system is mounted on a skid in the bottom of the unit, like you said. Looks like there's a front cover you'll have to remove, looks like there are some screws that will hold it on. Then you'll have access to the front of the skid most refrigeration units I've worked on have 2 or 3 bolts holding the skid in place. Check the front for these bolts. They'll go down or sideways through the metal plating, bolting it in. If you can access the back there may be some there as well. Unlikely, but possible. Can you post some pics of everything so I can help you better?