Would it be safe to build your own battery relocation box that could be seal and the vented?

My idea was to take a plastic tub, just large enough to get the battery in, then cut slits in it so that i could mount it to the spare area, silicone (unless there is something better) the slits to the straps for mounting, then use rubber garments as seals for the vent and battery cables.

An air tight system except for the vent. Would this be safe let alone allowed on the drag strip?