Empty and clean the inside of your tank.
Make cuts ¼ the circumference of the tank to make your door(s).
Add hinges and handles to your doors.
Add door seals using flat bar stock iron.
Purchase or build a stand to support the smoker.
Purchase or build your steel or iron firebox,about ¼ to ⅓ the size of your tank.
Cut and add a damper on the far side of the firebox to control the airflow to the fire.
Cut matching holes and weld your firebox to your oil tank in a typical offset barrel smoker fashion.
Cut a hole in the opposite top side of your tank and weld an exhaust chimney vent in place.
Use angle iron to create supports for shelving on the inside of your oil tank. Purchase Or build iron or steel shelves to hold the food.
Do at least 1 final cleaning and then a hot burnout to get rid of any remaining oil and/or chemical residue left in the smoker before you cook food in it.
Paint the exterior with a glossy heat resistant paint that will be easy to clean and wipe down.
Add any final accessories of your choosing.
Load up the firebox with wood and/or coals, cook some food and enjoy!