To make randomized chests in any chapter:
First download this fix to EA’s fe8 definitions; the command you want to use is CHESRANDOM, which is formatted like so:
CHESRANDOM EventID pointer [x,y]
Where “pointer” points to your item/probability list. The item list is composed of the item ID of a possible item, then it’s chance out of 100 of being taken, repeated for every item you want the chest to have, then ended by 0000. The chances for each item in the list should add up to 100 or unexpected things could happen.