You could try mounting a pvc pipe across the top under the lid with a couple ends from a closet rod screwed through the outside for easy removal of the rod. Or it might be easier to just make a vertical support with a piece of pvc from the bottom center striaght up with the lid center sitting on it. An elbow or something on the bottom for balance and you could remove it whenever. Drill a few holes so the inside gets a little circulation, and you can mount a thermometer etc. to it.