Stove pipe draft

[Demonknight]

maybe...but that sounds a lot like the wood stove setup my grandparents used (go up a couple of feet then out followed by another upward run)..so off hand I would wonder more of how high you ran the outside, maybe add another section outside and see how that does before chopping into the roof.

[soused moose]

Demons right, I think you need to get the outside pipe up a bit higher …that should fix your draft problem.
In my opinion …A straight shot through the roof is a good way of going about this but you’d still need to get the pipe up high enough to clear any obstructions that would keep your stove from drawing.
On our second bus ‘Home’, I had to add a full section of stove pipe to clear the little second story I built for our daughters bedroom….and make our woodstove work.

[eggman]

I would think about 2 feet above the roof line should get a good draft goin.

[Ryan Grimm]

Make your stovepipe taller. When you have a couple elbows in it, you add resistance to the heat rising out of the pipe...the example I'll give is like installing the exhaust pipe on a clothes dryer.
When I install a dryer for folks, the instructions state to keep the runs to a minimum, and that every 90 degree bend is the equivalent of adding ten (10) FEET to the exhaust.

Plus you may have one more factor:
when wind blows over a bus, it can add or reduce air pressure over the bus. That in itself can cause backdrafting problems. A taller stovepipe gets the top of the pipe above this downdraft, and helps solve the problem.
That's why building codes evolved about chimney heights over house roofs, to reduce or eliminate the backdrafting problem from house-induced downdrafts.

Hope this helps.....