The roof of a popup camper is often the ideal place to store bikes and other items. But figuring out how to do this is often a daunting experience.
My solution years ago was to install Yakima Track Racks. The installation requires drilling small holes into the roof, and then installing the Yakima push nuts. Once the nuts are installed and sealed, the track is attached to the nuts, which are now underneath the track. The track allows you to easily attach Yakima Towers and the plethora of accessories that can be added via the towers.