I have two models; neither yet finished, that have cut open panels. The gap is dealt with by gluing scrap styrene to one side (vertical) edge, and one horizontal edge of the panel that was cut out. I forget if I used Plas-Struc(sp?) or Evergreen. A 1/16" square strip works. If the plastic needs to be "bent", soften it by coating it with liquid styrene cement... the solvents will do its job in just a few minutes. Once the glue dries, add a skim coat of filler (if needed), then sand down the new plastic to fit.
I'm no expert, so I hope I make sense with the description.
As for the hinges, too late for one model, but the other one... I want to try this "Gen. II" design.