I am making a cake shaped like like a severed arm. My plan is to bake one cake in a jelly roll pan and another in a 1/2 sheet pan. I want to make bones out of modeling chocolate, laying those on top of the jelly roll piece and then covering with the 1/2 sheet piece. If I fill this cake with strawberry filling, will the modeling chocolate get mushy and not hold shape? The arm will then be covered in fondant so I don't want the whole thing to go flat lol!
Also, any creative ideas for covering the board? I've considered making it look like a sidewalk or hardwood floor.

Any thoughts or suggestions appreciated!