I made a jello mold oven with suggestions from "that other site" and added silicone to insulate the outside of it.  IMO, it made a big difference, especially in colder campouts.  You can buy a silicone baking sheet(s) set at Bed bath & beyond, or any where, that's just where I got mine, cut to fit.  You can use a rubber band on the outside of the silicone to keep in place, or "stitch" it together with wire.  Just push the wire thru or use needle to create holes.  It stays in place pretty well by itself, if sized right.  It is not melt proof thou, as I found out, and creates quite the mess if it gets too hot.   I think I posted pictures on here, can't remember thread name.