I agree with Mark about how to combine the turret and the main part of your model - try and build in layers if you can - there's no big rule that states that all polygons have to join up. Download a few of Craig Clarke's models in the downloads section and pick them apart- you'll get some great ideas from there. Looks very polygon heavy at the moment as well. But heck, as an experiment for a piece of software you are unfamiliar with, its pretty good. In my early days all I ever did was make primitives
