I apply my own Zimm useing Milliput white, so i am not really in a position to coment on AM zimm. Like with any thing else regarding historical accuracy, the choice is yours. At least you are making that choice rather than having a lack of knowledge on the subject.
Yes, i did have the sameissue, and with my other Panther last year. And i at least i know its not just me. I think somthing is out with either the angle of the width, eitehr on the top hull piece or the rear hull. I found some sanding did help, but not to much. And then just hold it in place.