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.