Theres a tute on the resources page of a guy who made water cans out of spheres. I think you could also use a sphere as a base shape, do some pulling around, then trim or bool off the piece you like to add to the model. It only becomes an issue when you go to "add" the pieces together...You want to keep the "Punch through" "boolean together" theory in tact instead of trying to model the surface to "An exact dimension" then try to get a bunch of little patches to join.