Boxes arent typically constructed from Spanish cedar.
I don't and never have. All cigars in the coolers are in boxes and there's no reason to line with anything other than aesthetics and aeromatics. If your cooler isn't full, it could help the Rh stability.
I have seen the pictures of various coolers, ammo boxes, and other containers converted to humidors that some people put Spanish cedar lining in them. Why? If you are storing boxes of cigars, and the boxes are presumably Spanish cedar, then why add the lining too?
Absolutely NO reason what so ever.....purely asthetics.