Probase is a super-strong and eco-friendly interlocking grid system for garden buildings, including: sheds, cabins and greenhouses. more info ecobearer - an easy-to-use and lightweight foundation pad.. Shed base kit. comes complete with: membrane, membrane pins, shed base grids. available in 5' x 4' or 6' x 4'. Probase plastic grids – simply slide together and lock with pins – it’s quick and easy to lay. this plastic shed base is suitable for most timber garden sheds, summer houses, play houses, bike stores and log stores. lightweight- easily picked up, carried and placed into position..