Crossword Puzzle Remain hidden

Clue: Remain hidden

Remains of the tray? (e.g. ASH with 3 letters)
Remains a bit longer (STAYSON with 7 letters)
Remain calm (e.g. DONTPANIC with 9 letters)
Someting poorly hidden (OPENSECRET with 10 letters)
They're hidden when they're open (POCKETDOORS with 11 letters)
There are six hidden in this puzzle in appropriate places (TREES with 5 letters)
One of the world's last remaining People's Democratic Republics (LAOS with 4 letters)
Preserves, as remains (INURNS with 6 letters)
Hidden hoard (e.g. CACHE with 5 letters)
Wait while hidden (LURK with 4 letters)