It amazes me that almost everyone thinks first of Dicor when maintaining an RV roof even though Dicor itself markets it for rubber roofs not the fiberglass roofs you find on most Winnebago motorhomes. Some Winnebago trailers do have rubber roofs.
Winnebago publishes sealant callout sheets that detail the sealants and caulking to use for each application on your specific year and model Winnebago along with some supporting information:
Also, here's a link to a recent Winnieowners discussion on this topic. Response #14 in that discussion gives some specifics on one member's experience with Dicor on fiberglass:
Use Dicor if you want, but I prefer to use something that's recommended by Winnebago. It's my understanding that you could even encounter a warranty issue if you develop a leak and have used a non-recommended product.
Whatever you choose to use, I recommend removing as much of the old material as possible, clean the area well and apply the new material neatly and sparingly. Despite what's shown in the video, it's never a good idea to goop new over old. You'll never see this on a well-maintained sailboat and they're in a much more leak-prone environment than RVs.