You could used thin white card but not sure how that would pan-out as the CB was used mainly as an under-structure (or skeleton if you will) to hold every thing up and in place to allow the overlay pieces to go in place.
If you make it out of white card, it can be reinforced using resin or bondo. The bio that I made here is currently being 'bondo-d' to remove any imperfection, reinforce it a lil etc.
Not saying that using white card can't be done - it probably can but I would go with cardboard. Cereal boxes are thinner than rigid cardboard but that can be used to.
Good luck my friend
Double H