I can see how a rubbermade trashcan could work well. Also, metal is fine to use IF you insulate it. I fabricated mine out of sheet metal, and then padded each side of the metal with a half inch of good foam and then covered it in black vinyl, for a total of one inch thick foam. It works very well, i posted on the results several years ago, but the intake temp was at least 30 degrees F cooler than the engine bay.
The disadvantage to using metal is that it takes a good bit of fabrication work and bracket making.
I'll try to find pics, the server isn't working right now
