Dave, my Extreme suffers from the same thing. I'm pretty sure any rotomolded PE kayak can get the bends. I have seen a Hobie repair video where they sealed all hatches and openings, then pressurized the hull with LOW pressure, high volume air through the drain plug hole. They then poured boiling water onto the entire area around the low spot, then quenched it with cold water once the low area looked corrected. I would think sun-preheat would also help. I would try a good shop vac's blower side for the air source, but have not tried it myself yet.
It is very important to set your rack's support pads only under reinforced areas of the hull. The scupper holes are usually the strongest areas, and the best spots for the pads. If you can't put the pads by the scuppers, pick an area that has tighter compound curves instead of a flat area. Compound curves are stronger than flats.
Good luck.
