Need your help

what size tent, where is the location of the diorama, what time frame these need to be answered.

WWI, WWII, Korea, Desert Storm, some other time or place.

more than one guard, guard tower, fence around the tent, you also could have a jeep or a truck in the backround, is it a base or a temp camp

is the guard guarding a tent or a prisioner, what is in the tent WHAT is the sniper's target and why, 

Why is there a single tent? Or are there more? Why is a sniper in that close? Plus the other questions above. You may need to rethink the idea to get a realistic story.

Ok, their is an american base not to far from the german base. The americans base is a very stratigic point, but are running low on suplies. If this base falls to the germans, it will give them a very good advantge over the allies. So the american commander in charge of the base sent a team of snipes to raid the german base. it is set in WWII times, and th german base is a resupply point.

In that case you don't want a sniper.  The shot and the guard falling over dead will alert the defenders and the squad of raiders will not be able to complete their mission.   

What you want is a single soldier sneaking up on the guard from behind -- with a knife.  Perhaps the attacker is hidden behind a stack of fuel drums or cases of ammo.

stacks and stacks of supplies would be needed, maybe a couple of German trucks filled with supplies, but since the Germans were running low on fuel, I would not have great piles of 55 gallon drums of fuel.

several raiders with knives sneaking up on guards, the sniper would be back up