Destroy 2 tents for 1 medal and the other 2 for the other medal.
Though I'm yet to achieve this, you must destroy the central tent at the front first, and then the tent on the far right next. One medal should drop down. Destroy the tent at the rear next, followed by the tent on the far left. The second medal should now drop down. Destroy one tent per go and do not use jetpacks to damage tents so that more than one can be destroyed in one go. Every time I destroyed the tent on the far left last (before I learned of this tip, which I've not yet tried), the Major has been angry for this tent being destroyed and did not give any medals.