If you remember spending some time in Tundra Express you came across a rather unsavory Tundra patrolman, named Will, who tries to kill you. After the fight the mercenary will drop an ECHO detailing the location of his arsenal of weapons, due to how awesome you are that you killed him.
You can find this cache in the midst of the varkid nest in the western region of the Tundra. You’ll find the lid to the weapons not far past the nest waiting for you to plunder it. Clear out some of the varkid, so they don’t bother you as you open the stash.
As the doors open a chest begins to rise. Open it to recieve your rWA-holy crap it’s a trap! Turns out there’s a hefty amount of dynamite ready to blow you up. Get out of the way before it goes off. Several psychos will appear to finish you off, but you have plenty of powerful weapons at this point, making their deaths come quickly.
Walk back to the chest and you’ll finally get your proper reward. So much for no hard feelings.
Item: random shotgun or assault rifle