Hey Neil especially, and anybody else who might care -

  I recently replaced all of the fiber-based cardboard air deflectors in my '85 with plastic "cardboard" stuff. It is used in making shipping dividers, and has the same structure as corrugated cardboard, but is made of some kind of styrene. It is mostly immune to automotive solvents, tho I would not use it to make a gas tank!

  I used the originals as templates, and traced out their shapes on the sheet of board. I cut the stuff with a big pair of scissors. I then used a hole-punch to put holes in the places I was going to attach it at, using zip-ties and screws.

  This stuff was easy to put in, easy to work with, cheap, won't degrade like the fiber-board stuff, and most important for you and your question, all went in without removing anything except the old pieces. Except the grill. And dropping the spare tire down.

  (delays in replies are due to digest accessability...  ...by me, that is!)