Yes you can keep them in racks, the only things is that if you spray and there is not enough ventilation, this can cause problems. So, just be careful about humidity, for an example, in plastic back, I always put a heat pad below the back and put a part of the water bowl on it to make some humidity, you can aslo put a back with Sphagnum moss that you keep humid, just make a hole in the lid so your Boa will be able to get in when he needs humidity.
I hope it helps, good luck with your BRB.