A while ago Ian Mcollum from Forgotten Weapons analysed an Al-Qassam-produced video showing a (supposed) underground armaments facility in Gaza producing anti-material rifles. He concluded that the facility shown in the video couldn't possibly have been used in armaments production, and that it was probably set up specifically for the shoot in order to not to give the Israelis any useful clues about the actual production facilities - which is pretty sensible.
The first rule in propaganda is to always ask, "Is the propaganda worth it?"
In a lot of these cases, it simply isn't.