Hi, a much cheaper alternative would be the Ewa Marine bag B-F100. I use it myself and had the idea to put the TS-E 17mm inside. Normally a 82mm filter thread is need to attach an adapter ring, which attaches to the clear glass panel in front of the bag. Of course the TS-E 17mm does not have any filter thread and putting it inside the bag results in lots of pounces of the lens to the glass panel. Not a good idea...
The solution is the LEE Filters Adapter Ring for the TS-E 17mm. It still does fit into the bag, although it is very, very tight. The LEE adapter ring has a similar effect than the Ewa ring. It keep the glass panel in a plain position a few milimeters in front of the lens. There is some slight vignetting but it is very small. The attached picture shows the vignetting with an f14. It is a RAW converted to JPEG. Of course every militer of shift will result in serious vignetting. Turning the manual focus ring is also pretty difficult. But it does work.
The Ewa Marine bag + LEE adapter ring will cost you US$500.