Before your initial cook, season it by wiping down the interior with any high heat cooking oil (vegetable, avocado, canola, etc.) and burn coals in it at 350 to 400 degrees F. This will give you an initial protective coating to prevent rust. As you cook on it, the grease and oils from the meats will continue to layer on a seasoning that will give you further protection.
Also, if you store it outside covered, you still want to keep the base of it raised off the ground. Place a couple of 2X4’s underneath it. The bottom is closest to the heat source, and over time the heat will take its toll on the metal. If the bottom gets rusted, it will disintegrate quickly.
But for the most part, keep the exterior covered, touch up any scratches, store it raised off the ground and you should be fine.
Have fun with it!