There are several tools that are made to help get behind the wheel faces to clean the barrels and calipers. Check this options out:
Wheel Woolies Kit
Wheel Woolies Caliper Brush
EZ Detail Brushes
My Go-To Wheel and Tire Cleaning Products by Zach McGovern
You have likely found that it is very difficult to protect these surfaces as well if you try to do it by hand. Thanks to some awesome inovation in the recent years, there are now spray on rinse off products that make this simple and easy. Check out the following products and article on how to seal your wheels in under a minute without any wiping or buffing.
CarPro HydrO2
Gyeon Wetcoat
CarPro HydrO2: Seal Your Wheels in Less than 1 Minute by Zach McGovern