Also make sure you walk rather than run while you are inside the base in German uniform or you will give your disguise away quite quickly. Use CapsLock to toggle between running and walking.
After I switched uniforms with the guy in the bunker, just before I snatched the truck, I found I could walk through the camp pretty freely and right next to other guards without raising suspicion. Watch out for the officers and SS guards in black though as they are capable of blowing your disguise much easier than lower ranks. You will need a black officers uniform to get anywhere near the safe unless you prefer a huge gun battle - or set up a diversion with your explosives
