> Why not put the entire enclosure on the balcony, and then heat-humidity control the inside of it?

How flammable is the insulation on your balcony? If you DIY it, then the danger of burning down your house might be bigger than the health risks of occasionally printing PLA in the living room.

Another option could be a used incubator, but an incubator big enough for a printer will probably cost more than the printer...