You can do this
in a local match
(not anymore apparently), though a public one works as well. I personally did this on cove. Be sure to set the rounds to LONG to give yourself extra time. When in the pregame lobby (where you can move around), press START and vote for the cove map. Chances are it'll be one of the other two (or a map from the map packs) if you don't. I don't know whether open just means open. I moved at least one item around from each chest just to be sure.
There's 13 chests in total on Cove.
Now their locations:
- 5 in the centre.
-In these rooms there's 3. One is in the room in the top left. You'll have to jump from the room in the centre, onto the roof of the room in the far left. From here, you can jump to the chest. The 2nd chest is behind the room in the centre, against the rocks. There is also 1 chest in the water in the bottom right corner. (almost against the rocks)
The chest in the water (bottom screen)
-In this screenshot you can see 2 chests. One is just to the right of the small creek. One is roughly at the nose of the skull shaped rock. Go to their eye, and then you can get to their nose.
-There's 1 chest inside the pirate ship, middle floor.
-There's 1 chest behind a tree on top of a building (Bottom screen shows location as seen from spawn. Top screen shows location when on top of that building.
-There's one chest in the building to the right of the skull shaped building. You can see the chest from the centre. There's ladders to take you up.
For those who prefer a video guide, Skycaptin5
made a video guide for the cove map, also showing all 13 locations.