Continuity mistake: Near the beginning of the episode, when Del talks about his Polaroid, there are no extras walking behind him. The shot changes quickly to Rodney, then to a wide shot of both Rodney and Del in which time the 2 extras walking in front of Vimmal have manages to walk down the stairs behind them.
Plot hole: Del and Rodney find the nuclear shelter and decided to try it out. They then do a couple of runs to find the best place to build it. We then see the pair inside the nuclear shelter which they have built, filled with stuff like a bed, food batteries etc. all in one afternoon.