Best Way To Preserve Covers?

I just won an auction for a nice fancy cancel cover (Ill add it to the fancy cancel thread when I get it). I am going through a number of my other 19th century covers and wondering the best way to preserve them. And Im not big on mounting covers like I have seen some members do.

At the moment I am using transparent sheet protectors that are in my duplicate binders. However, these are kinda thin and I don't know if the plastic will affect the cover. Anyone have any good ideas?

I've seen the card holders that you slide the corners of a cover into - but are these one size fits all, and then maybe put it in a sheet protector?

Lots of people like the vario 2S sheets for holding their covers. You can get them on ebay.

I use the Vario and like the quality very much. Another thing to remember is to put them away on low humidity days. It gets so hot and humid in Houston it can be a real problem. Also handling the covers is tricky. The oils and acidity from your fingers will attach the the covers and documents. You can tell the difference years later.

Thanks guys, I actually had regular vario inserts for my binder dups but never knew the brand because I got them at a yard sale. I just picked up some vario sheets for my covers. Thanks again!