Taking good care of and maintaining your BBQ and warming plates are important as they are the part that comes in contact with your food so you want it to be clean and rust free. Without some basic maintenance they can easily become rusty, dirty and piled up with ash from coals and heatbeads that stick to oil and grease which can be hard to clean.
The first thing you want to do is to strip back all the grease, ash and rust using some good old fashioned elbow grease. Generally a scourer or steel wool might be enough to achieve this but if your plates are in worse condition a rub over with a wire brush (either by hand or a rotary wire brush on a drill or even some fine grade sand paper. Get your plates back to the stage where there is no grease, dirt and rust or any other flaky bits. Give them a good wash with clean water and dry extremely well, you want zero moisture when you season them. Don't skimp on this step because ultimately the final finished product depends on how well you do this step.
Give a light coat of cooking oil such as flaxseed or canola. Rub oil all over gently with paper towel. You don't want too much oil or it will come out sticky, just a nice light even coat is best. Now bake in an oven or hooded BBQ at, at least 200c for at least an hour or until the oil has dried to a hard polymerized coating. Allow to cool then give another light coat and repeat process. Do this as many times as you would like but at least twice is recommended. When cool give a very light coat of oil all over to finish. This is something you can do regularly each time you fire up your Ozpig, give your plate a clean over and a coat of oil and put it on over a hot fire, the more you do it the better your coating will be.