I dont know how big you are thinking of having the lid but would you be able to use moulded rice crispy treats and then cover them with fondant. You can get the shape you want without it being to heavy and it will be edible. You could use a fondant covered long dowel each side to hold it up.
I always try my best not to have anything that isn’t edible on my cakes :) Good luck with it xx
ellie's elegant cakery
