I've been looking for a rucksack style bag to carry my Ansco 10x8 without much success. Camera bags never seem to be deep enough, and rucksacs don't seem to be wide enough, so on a whim, I called in at a fishing tackle shop last week to take a look at their fishing bags. They had quite a few bags that would have been suitable, but for £50 I bought one of these:
The 10x8 drops nicely into the main compartment, the front pocket is large enough for dark slides, and I can easily drop a lens on a 6"x6" lens board into the side pockets and put a dark cloth on top. The top pocket takes my light meters, spirit level etc and the whole thing is easy to carry with it's well padded straps.
If anyone else is looking at a bag for carrying their large format kit, then a fishing tackle shop may be a good place to look, and the cost seems to be much cheaper than anything you could buy from a camera or hiking shop.