The purpose of a fume hood in a Terraformation seed bank is to protect the seed bankers from any hazardous particulates inside the small space of the container. The main reasons to have one are if (1) any of the species you work with have poisonous plant parts, especially fruits and seeds, (2) any of the species you work with may create a lot of dust during processing, or (3) you expect to deal with a lot of mold. The best practice is to avoid collecting any seeds with mold, but some species and locations are more susceptible.
If your seed bank needs to purchase a fume hood for health and safety reasons, keep in mind that they usually have a long lead time for shipping. We also recommend that you contact the fume hood supplier directly and ensure you are purchasing the correct model and filters that will protect the user from particulates - rather than creating a sterile environment for the specimens inside (the latter is not necessary for seed banks).
Another option is to create an external but sheltered processing area on the outside of your seed bank, where you can process seeds without exposure to sun and rain, but with good airflow for any particulates that might be irritants. For poisonous plants or any more severe hazards, make sure all workers wear a mask that will protect them, to the degree necessary for your work.