For internal body parts use Body Wax by Wurth. You can spary with their Mulit-Sprayer or rig up your own. This is what many of the high end shops use during restoration. The link below takes you to a demo on the multi-sprayer. Wurth sells the Body Wax.
Product Demo|WURTH USA Inc.
https://shoponline.wurthusa.com/wurthusa/servlet/CyberVendor/category/G4235578/catalog/group.jsp/