Just picked up a Wolfman Express tank bag and it's perfect.
Four strap mount and is a flat design, not larger at the rear.
I have it mounted at the front of the tank and it's not in my way at all when standing. Plenty of space for a camera and is zipper expandable.
My only complaint is that the map area is just a little too narrow for a Bulter sized map. They sell a larger map holder that I'll probably get.