My mom is trying to save trees via newspapers, lol. She has all sorts of old papers and clippings. Also, I had been a journalist for a while, and saved my stories. In both cases, absence of light and air seem to preserve them better. A front page (or top of the pile in my mom's case) yellows quickly, but pages not exposed seem to do well. Exposed edges tend to yellow, though.
You could ask at your largest local library/university library - one that may have conservators. They may have some advice. You could scan them and have the files wet-printed at your local minilab, lol. Scanning and printing with a laser printer may last longer before yellowing. Scans might be nice, but then you have the perpetual back-up cycle do deal with.
Hmm... keep in mind what this website is about... you could make your own "microfilm" copies as well.