My lab is in my garage. My dirty dusty garage with two grow chambers with circulating air. A SAB would not be as effective for my environment so i went with a tyvek sleeve box. I used the sleeves of a tyvek suit attached to a 4" coupler to help seal and filter any air entering the chamber and weatherstrip to seal the lid. I've made over 200 lbs of spawn inside this with maybe 3-5 contaminated jars, mostly due to poor sterile tek and not the box.
Get the largest clear bottom tote you can find, make sure there are no scratches on the bottom and avoid scratching the bottom.
Get a 4" PVC coupler and bisect it. Cut holes for the 4" coupler and pre drill holes for screws, i used some sheet metal screws i had on hand.
Take a tyvek suit and cut the arms off, attach to the coupler with a SS hose clamp. I used gorilla tape to reinforce the stitching.
Make sure you have slack so you can reach the corners.
seal up the bottom with some cheap window foam weatherstrip, $3 from home depot.
Always wash your hands and arms as well as possible before use. Sometimes i would wear nitrile or latex gloves, mainly so my hands don't smell like bleach. I would spray down the inside with a 10% bleach solution before starting work. Allow 3-5 min for the air to settle before beginning work. When doing agar work i would include a self igniting blowtorch and use it as needed. After 4-6 torches the boxes oxygen is exhausted so i would throttle the flame for minimal flame. If i need to continue work i would crack the box and fan then allow 3-5 min again for air to settle. Once complete rinse with tap water and allow to air dry before sealing back up for storage.
In storage out of the way hanging off a screw.