Hi Jorge - We thought this question deserved a thread of it's own. The temperatures in a smoker are going to be a lot less than a rocket stove, and being in closer contact with food the issues are a bit different.
Welcome to Permies!
My suggestion would be to take one of these mini torches that are used for browning foods in the kitchen and burn off any residue that might be inside. Please use safety equipment like long gloves and glasses.
Maybe some of the more experienced folks will speak up with their suggestions.
You might find this helpful:
Invasive plants are Earth's way of insisting we notice her medicines. Stephen Herrod Buhner
Everyone learns what works by learning what doesn't work. Stephen Herrod Buhner
Food grade liners are often a BP-X material, which is a kind of plastic.
I know your food won't be in direct contact with the liner. I can't find a direct answer as to whether it off-gasses when heated, but I suspect it does.
Personally, I would remove the liner before using the barrel.