Demountable simple fume hood
Since the chemicals will not be in contact with the plastic for very long, very little will diffuse through the plastic. 

If you are concerned about fire, you could wrap the outside (not the inside) with aluminum foil; this should keep the fire contained. Have a container of sand handy in case the fire is extremely hot and the aluminum starts to burn. In fact, sand would be handy for most fires since it will decrease the amount of oxygen getting to the flames.

As long as you have a high air flow and the volatiles are coming from a small area, there should be no problem. Added: The concentration of the volatiles will not be high enough for a spark to ignite.

I can't really comment about the environmental effect unless you provide more detail. If the MSDS doesn't mention a hazardous exposure from the fumes, then you probably don't need a fume hood. You can get some activated charcoal (from a pet store) and pass the fumes through the charcoal, but I don't know how effective that would be.