90% of everyone here has the PCM exposed, its fine. When I wash my engine bay the only thing I cover is my filter (saved Wal-Mart bags work well lol). Do like I did, just get some single sided thick foam tape (insulation for door frames works well too), line the area where the stock intake box sat, place PCM there. It will hold, no vibrations, no worries.

However. If your so anal that you HAVE to have it protected, buy this and problem solved. Its costly and a waste of time and more restrictive than helpful, but works and flows slightly better than stock.
SLP Ram Air Cold Air Induction Airbox 1997-98: 3800 Performance