It seems to me that lower class people are most likely to be shown on daytime talk and "reality" shows such as the various Judge (Whoever) shows, though I'd question how real any of those representations are either. I did, however, want to respond to this:
they're not supposed to be accurate and meaningful--they're supposed to be funny.
I fail to understand why these two things are supposed to be in opposition. Rather it seems to me that humor comes from recognition -- when humor portrays the truth of a situation that is often either unspoken or overlooked in everyday life. And humor targeted at minorities is particularly rife with this evocation of common experience. Of course the lower or working class is anything but a minority, just like women aren't, but they are in terms of power within a society.
I'd agree that the SPN characters are supposed to be working class, but I suspect this has more to do with the longstanding practice in American culture of using lower and working classes markers to evoke masculinity than because it has anything to do with class itself.