Oil Drip Heater Plans?

So I did a little searching and could find anything on making a waste oil drip heater. I have seen several on youtube but no plans, tips, and improvments. Ive seen them done with brake rotors and propane tanks.

Does anyone have plans for one or built one in the past. the propane tank conversion looked nice. and the great thing is they are readily availible and i change my own oil so I have a ton of it laying around.