Just bought a '98 Cheyenne for a work truck that I'm pretty happy
with, appears to have been driven mostly highway miles around here
(Midwest).
 Most if not just about all of these trucks around here develop the
rust-out over the rear wheels.
 What is the cause/prevention for this?       Has anyone ever drilled
through the inner fenderwells to get to that area in between the walls
of the box and blasted a bunch of undercoating in there?
 Seeing so many of them rusted in the same spot would suggest there's
nothing can be done about it, but it seems like if a person took the
time they could at least slow it down a lot.  TIA