Since I never followed through with a resolve on this Thread I'm now including a follow up since eleven separate PM's have now originated with inquiries. This should at least showcase how I approached it, and hopefully help anyone that may visit this Thread in the future.
I never did uncover a skid plate for the front of an E-350 that effectively balanced the level of protection I was looking for with the ability to NOT restrict air circulation.
I ended up designing one I thought would check both boxes. Made it from balsa wood, then brought it to metal fabricator to duplicate out of 2" channel bar. The front mounts neatly to the underside of the Aluminess bumper, and the rear is supported by two brackets which attached to that beefy solid round steel bar which spans between the two sides of the frame.
Haven't had any issues with the fabrication or its stability. Only tested it once so far (by accident) when I rolled up (a little to far obviously) to a parking space stop made from the trunk of a fallen tree. No damage, and it performed as intended...at least I know it works.
Couple Pic's: