You don't bend at a 90 degree angle for the gun so it doesn't matter. I am contimpating this same question today. I made a gun with plastic, and filled the curve with bondo. But it all flaked away, and the plastic fell apart! (well I forcefully pulled it apart.)
They I made a new test gun. I took some spare plastic, cut it out.. and bended it along the curve. Much better method to make it. Although I didn't like that.
I then made a new cardboard gun. From a small section of a box, I took a cardboard piece and cut it out carefully using my dimensions and calculations. (There is some rather tricky math to get the right amount, and still have it curve.) and I glued that all together, and started making holes and other things. It is coming very nice, and is pretty strong.
But the plastic method is much better, so we will be making a new plastic gun in the future, using the heat and bend method. Now if only I could figure out how to get this bondo to stick.