Out of necessity, not being able to ship Todd's dust and pellet's here without them being sprayed with insecticide, I built a smoke generator, ...before I started I read all that I could find about what causes creosote, ...simply put, creosote is caused when the smoke is cooled, so..., because of aluminum's heat dispersing properties it's a bad choice for a smoke generator, the aluminum is transferring the heat inside to the ambient temp outside, if the ambient temp is cold then the smoke is cooled before it ever leaves the generator creating creosote.
I built mine out of 4", 1/8" wall square steel tube with a brass connector and I don't have any creosote problems, however my ambient is always around 80°, so if you live in cooler climates I would suggest a thicker walled steel pipe, ...think about it, a fire box uses 1/4" - 3/8" steel to retain the heat, I thought it should be the same principle for a smoke generator.
I hope that helps.
Gene