I have been lurking on this great discussion all along. I haven't seen much talk about a simple sprayer called a Preval. It is a self pressuring paint sprayer that you can put your own paint in and spray! I have been experimenting with this Preval and noticed that you must dilute the paint very thin (like water) in order for it to spray nicely. I even removed the small pre-filter in the pickup part of the spray tube in ordr to get the paint to work better. I have left paint in the lower part of the sprayer several days, and it hasn't hardened or gelled yet. May be an answer to reaching tough spots, or even to touch up as needed. Check it out and see what you think!