I don't want to sound like I'm defending the acid or anything but..
If you use it like you would any other product, be careful, spot test, etc. you could use it with no problems. Sometimes using acid vs. polish will even give you better results becasue it does not etch or dull the surfice of the steel.
If the waterspots are really bad, you can save so much time with the acid method. I would still reccomend taking the box out of the truck first, and spot testing.
Does anybody else use a wheel type acid for cleaning chrome, glass, wheels? It is wonderful, works really awesome. I have used it on ym shower doors, it is an awesome tool, and i did take the doors outside for this.