I have the Evans Walker. It can fit one body with lens, two or three other lenses, lightmeter, small notebook (i.e. paper not computer!!) film and other small bits. It can also fit 2 M bodies with lenses attached. I've even used it to carry a Rolleiflex and a bunch of filters.
It is certainly showerproof apart from the open side pockets of course.
It is a great little bag. The strap is a nice width and comfortable to lug around. Over time it loses its shiny newness and looks less like a purse/man bag.
MP, M2, M9, CLE
28 Ultron, 35 Summicron Asph, 35 2.8 Summaron, 40 Rokkor, 50 Summilux Asph, 50 collapsible summicron, 75 Summilux, 90 Rokkor