It seams like the 80's and early 90's blazer rust less then the 70's. Did they make any changes to the sheet metal?
If I'm not misstaken, GM used more galvanized metal in the 80-90's than in the 70's.
I rarely ever see a 90s k5 rusted.
Which is why I went all the way to Seattle to get my '89.
(Yes, I'm leaving the state shortly, shouldn't have to deal with the rust near as bad where I'm going.)