Got the bag! Sam at Detours figured out a way to get it shipped to me FAST. It fits my bike like a charm (it was a concern because I have a small bike and 38 cm handlebars) but it's actually quite small. My 300mm lens won't fit in it, and even the 18-55 is a tight fit on a small-ish Canon Rebel XT body.

I'll carry the spare lens in a special lens bag in my Carradice saddlebag and hope for the best. Otherwise it just never gets used, so I'll deal with the risk rather than have no chance at all to get pictures of those flamingos in the Camargue park.

Pics in two weeks.