I think there was a shift between S1 when I think the producers were trying to signpost Mac as working class (or at least lower middle class) and were succeeding about as well television ever does--which is to say not very much--and in S2 they stopped trying for the most part (and in S3 the divisions were erased completely).

I mean, without a doubt it's frakked up that because Mac's family went camping instead of skiing for vacations we are supposed to be reading them as poor, but I do think that we were supposed to be reading them that way nonetheless, as little sense as it makes.