A great way to stop camping is to make ammo cost money, If you buy the weapon you get the gun and no ammo, and ammo costs 1-10 cash a piece depending on the weapon, that way if humans are camping and the aliens are smart enough to not die, they will soon be left with no ammo no cash and generally hopeless.
The only exception being if you spawn with rifle, in which you still get default ammo, but once you use all that ammo you need to buy some to get some more. I understand that this isn't a stop to camping, and would probably need some balance tweaks, but nevertheless it would probably bring down the camping on humans alot.