2 20x3mm round magnets need to be used for the bottom.
i also used rubber feet to stop it from sliding about
100 PCS Self-Adhesive Bumper Pads Hemispherical Shape Noise Dampening 8mmx4mm Rubber Feet for Cabinets, Small Appliances, Electronics, Picture Frames, Furniture, Drawers, Cupboards. (Clear) : Amazon.co.uk: DIY & Tools