How do I work with math.random??

The purpose of this script is for every five seconds, it calls on a function which should randomly select a chest/part out of a model, and then it should randomly pick a brick out of a model which sets the chest's position to the randomly selected brick.

Basically, every 5 seconds, a random chest/part spawns at a random brick's position. Except it's not working, and it's been erroring with this;

21:57:38.685 - Workspace.TemplateLoot.LootScript:5: attempt to get length of global 'ChestMeshes' (a userdata value)

Here's the script;

ChestMeshes = game.ReplicatedStorage:FindFirstChild("Chests")
ChestSpawns = game.Workspace:FindFirstChild("ChestSpawns")

local function spawnChest()
local newChest = ChestMeshes[math.random(1,#ChestMeshes)]:Clone()
return newChest
end


local function randomSpawn()
local randomSpawn = ChestSpawns[math.random(1,#ChestSpawns)]
return randomSpawn
end


local function final()
local newChest = spawnChest()
local randomSpawn = randomSpawn()
newChest.Position = randomSpawn.Position
end


while true do
wait(5)
final()
end