Unless you have experience or know what you are doing I would strongly advise you not to attempt to modify your existing gas system.
I have seen the devastation exploding butane can cause and I don't want to be reading about you in the news.
Now, about woodburners in vans, sheds, yurts etc Check out http://windysmithy.co.uk/html/woodburners.htm
He specialises in light weight stoves for such applications and if you scroll down near the bottom of that page you will see the fittings you need to take the flu through the roof
If you are interested in Self Reliance, Frugal Living, Gardening and becoming Debt Free, follow my Blog tinyallotment.wordpress.com