The hull proved in my 1/700 HobbyBoss USS Boxer kit was twisted and bowed up in the center quite a bit - about 2mm. I thought the hot water method would be the best way to fix it, although I've never tried it before. I bought a metal pan with a flat bottom large enough to hold the part. First I tried soaking the part in not-quite boiling water, not quite fully submerged, and weighed with wooden blocks which were removed once the water cooled. That removed the twist, but it made the bowing even worse. Not wanting to abandon an expensive kit, I kept trying, upping the temperature each time. The fourth try - with water at a rolling boil, the weight increased by a soup can, and the weight kept on overnight - finally removed the bowing.
But it caused a new problem: the sides were now wrinkled along their lengths.

In fact, it was so bad none of those boxes installed internally could fit flush, and you can see they are pointing all over the place. The flight deck is thin, and its gluing edge too small to fix it. So I cut a slice of very thick 3/32in plastic sheet to the right size and glued it in a bit at a time using velcro straps to hold the hull against the form.

I had to cut out holes for the indented elevator sections, but fixing the sides close to the elevators didn't fix the elevator sections themselves - they were still bent in. I had to force the elevator sections out with 3/32 thick plastic shims.

And now it looks like it should and the flight deck fits. Hopefully this example will help other modelers.