made a box for mine yesterday, using some fiberglass sheets that my dad had in his shed.
started out out useing a sheet of card board, and cuting it to shape to use as a template.
once we had got it to the right shape we bolted it in place useing the mounts for the old air box, and then filled in the gaps with silicone.
then made a lid that screws in to place.
then painted it.
done, took about 5 hours total.