You are looking for a box covered with stones - follow the coordinates and check on the obvious location. The Military Unit near-by is not much active, it suppose to have a shooting practice field, but never heard any activities around there.
While you are going back to your cachemobile you may see (on the green zone) some Bunkers / Pillboxes / Fortresses - I didn't hide anything there because of the environment. You may visit these Old Military sites on your own risk - the area is mined with human excrements.