I agree with Poconos. Our panels are cross strapped with tie downs between every panel and locked down to the roof at the input/return headers. All of the piping is also strapped to the roof. The contractor used LOTS of silicon on every screw and all of the screws are stainless (I checked myself).

As for the vacuum breaker, you need that to allow air to reenter the system when you shut it off. A roof mount system "drains back" into the pool, without a vacuum breaker, the water in the system stays there. With a vacuum breaker the weight of the water column in your pipes will pull the breaker open, allowing air to enter the system which will allow the water to drain off of the roof back to pool level. (In reality, if your pump is running and your solar valve is OFF, the water level in the solar system will be higher than pool level because of pump level pressure going back the return line, but this is still going to allow the water to drain off of the roof).

As I said, go to powermat.com and check out the diagrams. The first page has a great animation that shows how a correctly constructed system fills up when starting, how it runs, and then how it drains back when turned off (which shows how the vacuum breaker works). There are also other animations/pictures that show how incorrectly setup systems will not work properly.

I wouldn't even think of starting to put up the system until you really understand how they should work and you have all of the proper pieces.