When I first got the filter..I had grand plans to get an extra plastic underbody piece from one of the many donors in a junkyard. Then cut/bend and mold it into something that would provide protection. A 95-99 front splash shield seems great because it'* already two layers with air holes so that water can't splash in.

Mines rubber, not plastic. It makes is easier to manipulate into shape.

On my 98 I used vynal (or what seemed more like rubber from my memory) stairstep covers.

Walk into Lowes or Menards and you can locate these. Then use double sided industrial tape to keep them in position below your filter. Just stick these "mats" on the areas of the lower part of the bumper where there is a lot of the road showing.

After the entire length that I had my 98 I only had to clean the K&N cone filter once, and I live in northern Illinois where the snow lasts 6 months out of the year.

K&N actually has a water resistant sleeve you can put over the filter. It'* some sort of fiberish material, but resists water. Might not be the answer you're looking for though.