bending styrene

Dgb.;

   I would recommend aligning the sides as you fit Bulkheads .The plastic is NOT the same thickness throughout the model . It's a fact of life here .You can adjust the bulkheads easier that trying to align the two halves with any kind of heat .

 If you have a LARGE machinist Micrometer then you can measure the thickness throughout and sand to your heart's content . This is usually is not the case .

 If you carefully build your bulkheads and interior to fit as an open sided tube That will slide into the hull without binding Then you are halfway there . Then you can fit Shims of .010 into the hull between the interior and the hull till everything lines up .

   This is the way I do all client  "cut away'  models . It's easier and looks fantastic when done . Plus , leaves room for adjustment as you add more parts .    T.B.  

Got it, look before you... Anyway the observations. The hull halves juxtaposed with no constraints are in slight misalignments along seam. Hull halves juxtaposed with rubber bands, all seams in alignment. How to heat parts below damage range into slight chrystal lattice realignment. Oven questionable, water below 170 F no problem, but results?  It very well might not be possible. Why is there air?

I'm not sure exactly what you're trying to achieve but heating it in hot water, let alone inside an oven isn't a great idea. You're likely to warp and melt the plastic thus ruining it.