I built a horizontal drum smoker for a friend using a 55 gal. drum and a 20# propane tank for a friend. I went to the muffler shop and had some exhaust pipe bent to connect the firebox to the drum and for a smokestack.
It worked great, but I had a welder to work with. Maybe you could get the guy at the muffler shop to weld you something up. The smoke pipe wouldn't have to go into the bottom of the drum, just below your cooking grate.