Storing Jumbo Covers

Hello all,
I received this lovely registered cover in the mail yesterday from londonbus1 along with a few others of identical size. It barely fit in my flatbed scanner. So my question is how do you store your giant covers? This one measures 11.4 by 6.1 inches, or 29 by 15.5 cms. It doesn't fit in my vario binders or my cover binder. What is the best solution that is still cost effective? Having a slipcase is important to me, it gives that extra layer of protection. Here are two scans of the beautiful cover. Don't you just love the wax seal.

This is a horizontal view.

An album slipcase might, in fact, be the answer. A White Ace slipcase measures 10.0 x 11.6 inches (interior), and it would hold 20 big covers comfortably, I think, stored on its "spine". Lay a cotton cloth over the top to keep dust and insects out.

No slipcase here, but this is what I use to store my oversized covers (and a host of other philatelic and non-philatelic material) that I want to keep flat, clean and away from the elements for long term storage and they work great, plus they're available in a whole host of sizes to fit most any items up to small posters. Another advantage is that they are typically available from most craft stores (i.e. Michael's, Hobby Lobby, AC Moore, etc.) and with on-line coupons for up to 50% off a purchase, the price can't be beat:

http://www.artprofolio.com/Art_profolio.htm

I also use Itoya Art Portfolios for my really big items. The sizes I use are 9x12, 11x14 and 11x17. I was made aware of them on this forum.
Regards, Robert

The USPS sells a looseleaf binder with lots of holes for commemorative pages which are a little larger that 11" and they might work.

I use common everyday sheet protectors, 3 ring type, and put them in there.