FWIW
I tried a printer enclosure similar to your picture with the sides and top made of fibreglass sheet. It was always a disappointment in that it did little for the warping/distortion that I encountered.
I then found out some further information about Prusa. Allegedly his print rooms are kept at a very high temperature, around 28-30C.
So in a final attempt to resolve the warping issues I constructed an enclosure with foam insulation board, the type with silver foil on both sides, stuck together with silicone sealant. This easily reaches 30c with just the waste heat from the bed. I leave the door open a bit if it looks like getting too hot.
The print quality, and strength is amazingly good using this technique. Even printing in a garage at 0C recently the resulting prints were outstanding. (Marlin blew up with lowtemp but its fixable by using a hot air gun on the bed for a few minutes prior to a restart)
This sort of leads me to the conclusion that it is not the drafts which cause the problem but the ambient temperature at which the print is being made. It may be a combination of both, but for me the major effect was ambient print temperature.
Hope this helps
Best Regards
picclock