Unmarked vans drive around all the time. They don't typically park out front of a whistleblower's house. There is more scrutiny there than driving down any random street. Therefore, a more sufficient cover would be required.

An unmarked van could park in front of any arbitrary public neighborhood house with street parking for a few hours and nobody would care. As long as people aren’t visible in it.

Multiple days would be suspicious but that would be true of even the “sewer inspection” cover van

An unmarked white van (without windows) parked a house or two down the street hacking your wifi might not be that noticeable. One across the street with a radio dish spinning around and a parabolic mic sticking out the window and a few people entering and exiting it with donuts and coffee multiple times probably would be.