We have a Sportsmobile Sprinter 3500 Extended Length van, 2wd only. It is the medium height model (about 6' 3" inside, I believe). We have a roof ac, Fantastic Fan with vent cover and a Winegard TV antenna. It was 9'8" before we added the roof vent cover. I think it is about 9'10" now. It lives outside year around, but since it is our second car, it is driven year around.
You will need 14í wall height to get a 12í roll up door.
You can get an idea of the problem doing that with this garage, the slope of the roof above the 16' wide overhead door. I'd have to break it into two openings and leave the near side with the existing 7' header in order to open up the far side to 10' or more height. Not impossible, but I'd really have to want that tall opening to proceed. I have not measured precisely to see what's doable but that project is waaay down the list.
The finally-getting-underway project.