I'm assuming there's a spring loaded shaft with cable spools on the ends like a garage door?Yeah it's a pretty heavy door. I honestly don't think I could lift it without the assist. It's really not even what I would call easy with the assist.
I built a 7x12 box trailer in the fall of 2008 but winter set in before I could come up with a practical idea for the door so I just slapped some barn siding and 1x4's together to keep snow and stray cats out of it. It's been like that ever since.