I would seal the lid on, maybe adding some vents, cut out most of the front (leaving intact sections at the bottom and top for rigidity) then replace with hinges to make a large door.
Add some wire shelves or hanging bars for jerky.
I'd use a gas burner in the base underneath a wood chip tray as the heat source. A small chute running through the barrel wall into the wood tray would enable you to top up without opening the barrel door. Blanking this off when not in use would obviously be useful to limit smoke loss.
Finally, mount a dial thermometer in the door section and I think you'd have a pretty serviceable smoker.
The only thing is you'd get a lot of heat loss with no insulation, so it might be a bit gas-thirsty maintaining temperature.
