Acetone works. I used Eternaclean. It ranks up there with brake cleaner. It works quick and flashes off real quick. And yes, prep is a must if you want it on long term.
Here is my install
Eternabond Roof Seal Tape on a Sunline (Lots of pics)If I ever buy another camper, it it will get the same treatment shortly after I obtain it.
See the Eternabond site for instructions on the cleaning and application.
I have also applied a thin edge of Dicor on the exposed edge on the roof to help stop the dirt from sticking to it over time.
I also did the slide seams.
Hope this helps
John