That's a very nice model!
On Brsseb's car and boat tutorial, it tells you how how to do a gunner and driver e.t.c, so I suggest you read those to find out how. Also, I'm not sure about this, as I have only made static objects and a few weapons, but weapons need to be made facing left, so if the same applies to vehicles, which is what your model is classified as in OFP, then this might be a problem.
Try these out and see if they work.
TMan10K