2 tips from an experienced rack builder.
1) this is ESSENTIAL! the space above your rack tubs is too large and I guarantee you, your snakes will escape the tubs easily if they want to. The space needs to be very small unless you have tub lids, which are cumbersome.
2) not as essential... that plywood will get moist and warp or maybe even mold. So what I did was waterproof the boards with deck paint.looks pretty good though.