Roblox perfectly sized Viewport Frame with model rotation

perfectViewportFrameRotate.lua

-- Perfect ViewportFrame Script with 360 degree Rotate
-- thanks to @sleitnick https://www.youtube.com/watch?v=2J-2v_UqNDw for the hard part
-- Put this code in a LocalScript inside of a ScreenGui in StarterGui
-- Change the reference to the model a few lines down to point to your model
-- Delete rows 40 and below if you don't want the rotate code

local makeModelSpin = true -- change this to false to keep the model stationary

local viewportFrame = Instance.new("ViewportFrame")
local camera = Instance.new("Camera" , viewportFrame)

-- Set model
local model = game.ReplicatedStorage:WaitForChild("Troop Carrier"):Clone()
model.Parent = viewportFrame
model:MoveTo(Vector3.zero)

-- Set viewport frame
viewportFrame.Parent = script.Parent
viewportFrame.CurrentCamera = camera

-- Determine camera position / using logic from https://www.youtube.com/watch?v=2J-2v_UqNDw
local orientation, size = model:GetBoundingBox()

local rot = CFrame.Angles(math.rad(0), math.rad(90), 0)

size = rot:VectorToObjectSpace(size)
local sizeX, sizeY, sizeZ = math.abs(size.X), math.abs(size.Y), math.abs(size.Z)

local frameSize = 500

local h = (sizeY / (math.tan(math.rad(camera.FieldOfView / 2)) * 2)) + (sizeZ / 2)

local frameX = (sizeX > sizeY and frameSize or (frameSize * (sizeX / sizeY)))
local frameY = (sizeY > sizeX and frameSize or (frameSize * (sizeY / sizeX)))

viewportFrame.Size = UDim2.new(0, frameX, 0, frameY)

-- Set camera position
camera.CFrame = orientation * rot * CFrame.new(0, 0, h)

--======= ROTATE 360 ========

local TS = game:GetService("TweenService")

local function tweenModel(model)
	-- set PrimaryPart to center of model to allow for a smooth rotation
	local centerPart = Instance.new("Part")
	centerPart.Material = Enum.Material.Neon
	centerPart.BrickColor = BrickColor.new("Cyan")
	centerPart.Size = Vector3.one
	centerPart.Position = orientation.Position
	centerPart.Transparency = 1
	centerPart.Anchored = true
	centerPart.Parent = viewportFrame
	model.PrimaryPart = centerPart
	
	local CFrameValue = Instance.new("CFrameValue")
	CFrameValue.Value = model:GetPrimaryPartCFrame()

	CFrameValue:GetPropertyChangedSignal("Value"):Connect(function()
		model:SetPrimaryPartCFrame(CFrameValue.Value)
	end)
	
	local tweenInfo = TweenInfo.new(
		2, -- Time
		Enum.EasingStyle.Linear, -- EasingStyle
		Enum.EasingDirection.Out, -- EasingDirection
		0, -- RepeatCount (when less than zero the tween will loop indefinitely)
		false, -- Reverses (tween will reverse once reaching it's goal)
		0 -- DelayTime
	)	

	local tween1 = TS:Create(CFrameValue, tweenInfo, {Value = model:GetPrimaryPartCFrame()* CFrame.Angles(0,math.rad(120),0)})
	local tween2 = TS:Create(CFrameValue, tweenInfo, {Value = model:GetPrimaryPartCFrame()* CFrame.Angles(0,math.rad(240),0)})
	local tween3 = TS:Create(CFrameValue, tweenInfo, {Value = model:GetPrimaryPartCFrame()* CFrame.Angles(0,math.rad(360),0)})

	tween1:Play()
	tween1.Completed:Connect(function()tween2:Play() end)
	tween2.Completed:Connect(function()tween3:Play() end)
	tween3.Completed:Connect(function()tween1:Play() end)
end

if makeModelSpin then
	tweenModel(model)
end