The fit on this kit and the BMP-1 (just a few parts swapped/extra) is real loose. Decide whether or not you want the hatches open or close. Those oversized working hinges don't really work. It's best to glue the hatches and hinges in place. I found the upper hull went together really tough. I had to work those edges of the hull towards the rear.
For the periscope, you can use something called "Crystal Clear", it's a watch makers' glue. You can also use clear drying 5-minute epoxy or for the budget minded, just use Elmer's white glue.