PLA doesn’t “need” it to trap in the heat, but an enclosure would help in trapping any fumes and then you can add a vent to the window to suck those out with a fan. Depending upon how fancy you want to get and how much money you want to spend, you could just buy some cheap sheet metal ducting from Depot for cheap and attach it to the window and then attach the other end to a plexiglass enclosure. Some people use the LACK IKEA side table as their frame and attach plexiglass sides so you can still see the printer working. Those LACK side tables are like dirt cheap at like $15. Or you can build your own.
I’ve never bothered to build an enclosure simply because I can just change the time when I do longer prints. If its like 15 mins I don’t care too much, but if it like a 10 hour print, I’ll do it at night usually.