if i was u ied build 5 sides of the box n just mold the front how u want with fiber glass, tim put nylon rope in his box to help strength wise, ied atleast try to get it 1/8 thick or more
why i say he put rope cause it helps conture to curves n add structural integrity too, ied make some rings, n then put supports to em to back of box n then go from there
just make sure its alteast 1/8 thick with a good base print, when i fiberglass i go fleace, resen, mat, resen, mat, resen, mat n then resen n should do fine, i unno how many layers but just make sure theres not many if any bubles in ur resen when it cures or u'll halfto build that spot up
anyways good luck wit this