to do this you have to get he first thunder gun out of the box
there are 6 total red boxes around the map and 1 fuse box on the pole in the ally. 1st you have to knife the boxes in this order: lobby, fuse box on the pole, fire trap room, the 2 in front of the stage, in the dressing room window.
1st red box next to the quick revive in the lobby
2nd box (fuse box) out on the pole behind the trash cans
3rd room in between the ally and the lobby on the floor in the middle of the room (fire trap)
4th in front of the stage on both sides next to each window
5th in the dressing room across from the mirrors behind the the window on the right wall theres another one behind that window on the very back wall to the left (those you have to shoot
if you do it right it will shoot out blue sparks
it was hard and took awhile to get the thundergun out of the box but we finally got it
after you do this the more and more you go to the box the more you will see it and have a better chance of geting it

dont knife the boxes in the order the video shows
this isnt me but it helped me find all the red boxes
if this helps be polite and thank me