My chimney is around 8'. While not a perfect install, it works just fine with our small stove. Before opening the wood stove door I open the intake air fully to get it burning as hot as possible to increase draft a bit. If I open it when it's burning cooler I sometimes get a small cloud of smoke wafting out the door.
I used Selkirk's twist-lock pellet stove pipe for the 5' extension on the bus roof. That way it stays on nice and tight and is easy to pop off.
It holds tight enough to stay on when cruising down the road at moderate speeds
Not advisable, but sometime you forget about the pre-trip checklist!
You can see more of my woodstove install in my build page, which is posted as my signature.