The Aprilaire 4732 is the correct replacement for the Aprilaire Model 700A Humidifier & Aprilaire Model 700M Humidifier. 

 The Aprilaire 4732 Base is a gray plastic base that attaches to the ductwork of your furnace. This base replacement is designed to fit selected whole house Aprilaire 700 humidifier series. Each side of this humidifier base includes swing locks. The approximate inside dimensions of the Aprilaire 4732 humidifier base are 14 7/8" x 14 13/16."  

This humidifier base does not include a solenoid valve. The valve is sold separately.