Both times we planned to go to Rose Blanche the weather did not cooperate and we decided it wasn't worth the trip in the fog and rain. It is still on our bucket list as we hear it is beautiful.
There is a provincial c.g. very close to the ferry dock. We have stayed there. We have also stayed at the provincial tourist info building which is about 10 km. down the main road. They open early in the a.m. and it is the perfect place to get travel info for the entire island. This works well if your ferry docks late at night.
Enjoy your trip - it is a wonderful experience.