Ok I'm sure there are different variations of this, but I've been playing around with this one, and it seems to work ok. I've placed this on the on_death and on_open scripts of any chest and it works to some degree. I will flesh this out somemore to actually respawn the container as well (though I'm still a newbie in scripting).

1. Chest Respawner

2. Respawns random low treasure into chest.

3. You can uncomment parts of the script to lock chest.

4. The Script itself

NWScript:

//::////
//:: Treasure Re-Spawn Script
//:: Copyright (c) 2001 Bioware Corp.
//::////
/*
Spawns and Respawns in general purpose treasure, usable
by all classes.
*/
//::////
//:: Created By: Raasta
//:: Created On: July 6 2002
//::////
#include "NW_O2_CONINCLUDE"

void main()
object oLastOpener = GetLastOpener();

float fDelay = 30.0; //How long before the chest will respawn

DelayCommand(fDelay, GenerateLowTreasure(oLastOpener, OBJECT_SELF));

//::////
//
// The following command can be uncommented to make
// the chest lock after being used.
//
//::////

//DelayCommand(fDelay+0.5, ActionDoCommand(SetLocked(OBJECT_SELF, TRUE)));

ShoutDisturbed();

}