:I make my racks from One by three pine.. I stain it, and varathane it..The majority of the top opening is screened with simple aluminum :insect screening, and NO they don't rub.. I've used this system successfully for 16 years..Along with excellent ventilation, It's also light weight and that is another big bonus. :The entire units can be wheeled from one room to another for brumation etc. :The trays slide on their lips rather than their bottoms, and this also reduces wear on the trays and wood.