At this stage of the game your best bet is to not worry about it and enjoy your truck. Perhaps, looking on the bright side, if it does crack in the future, you can repair it then and you will know what not to do. I realize that it's a small consolation.
Currently I'm turning a Model A Ford 4 door into a 1/4 truck. The back section of the 4 door car was turned into the back of the cab. It was a lot of shrinking, stretching, hammer and dolly work but when it was done, a minimal amount of filler was used. All I'm really trying to say is that the extra work put into getting the sheet metal in the shape it needs to be pays off dividends when it comes to the longevity of the vehicle, not to mention the peace of mind knowing what's underneath that shiny paint.
I asked you who gave you the advice on how to straighten out the roof of your truck. The reason I asked was because quite often advice is given and sometimes it's incorrect. There's nothing wrong with questioning any ones advice or getting a second opinion. A rule of thumb if you question someones advice and you have any concerns and they say "don't worry, I've done it hundreds of times and never had a problem", get a second opinion, it's difficult enough to get through 20 jobs, doing things correctly with the same procedure and products and not have problems.
In the auto body world, there are painters and there are applicators, the painter is the person that cares about every job they do and takes pride in workmanship and if a problem arises, often has the knowledge and the ingenuity to fix the problem in the paint booth. There are body guys and then there are technicians, the technician understands how metal reacts with respect to impact (collision), heat (welding), fabrication (putting metal into the shape required for a repair or custom application) and has an understanding of current products and how they should be used. A body guy gets it close and carves the shape of the vehicle with the filler of choice. Just so you understand, there is nothing wrong with filler when used properly within the tolerances set out by the manufacturer.
I wish you only the best with your vehicle.
Last edited by 69 widetrack; 02-13-2013 at 08:15 AM.