With regards to the sail pulling out the rear of the bag, most modern bags have one or two nylon straps that are sewn across the back of the back (forming an "X"). in the center of these straps is a brass grommet - you run the snuffer line through the grommet before going to the sail. The grommet will stop the sail from coming out the back of the bag.

There's a post on here somewhere where I put an image of how to measure the spinnaker for a snuffer line - but I can't find it for the life of me.