If you get a low pressure regulator with a needle valve to minutely adjust the propane flow is a good start....
Size and style of the burner...
This burner, From Northern Tool, has 3 separate burners to adjust... It should cover all your needs....
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You will probably only use the smallest burner and need to adjust the gas flow to get it low enough...
Think about installing it under the smoker and have a pipe for the heat to travel through...
I would use the Amazing pellet smoke generator for making smoke... It would go inside the smoker.... The 5X9... get some pellets...
Hickory, Oak, pitmasters choice, apple, alder for fish... Get the big bags, a much better price + if you order now, there's a 25% discount...
A-MAZE-N Products builds and sells quality BBQ Smoker Tubes, smoker boxes, fire starters, wood pellets and Q-MATZ for gas, charcoal, and pellet grills.
amazenproducts.com
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