It's actually easier to solo.
Search for the two big rock formations as you approach the ammo crate from the South. There are two of these rock formations not far from each other, use the one the left (West) because he can't shoot you from the Southern direction & also not from East or West thanks to the rocks on both sides (it's a bit more tricky with the rock formation on the right (East) since he can attack from all angles.
Stay crouched between them & just focus on shooting him (with either high damage assault rifle / LMG (don't bother with noise suppressors, you wanna deal as much damage as possible) when he spawns in your line of sight. Just camp there & be ready to move when he aims/ throws grenades, then move back into position. Using Thermal vision worked best for me (and I'm a noob who only started playing over a week ago!).
I also tried planting mines & C4, but it seemed as if he adjusted his attack style & got more complicated. I had much better results without using explosives.
Good luck Ghost!