About a year and a half ago, I had some rust repaired on the quarterpanels of my 1999 GMC Jimmy, and then had rhino lining applied along the lower sides of the car from front to back. Now the rust is coming back through the rhino -- most prominently in the same spot as the previous rust on the passenger side, but also a little on the drivers side.

What's the best strategy to attack this on a budget? Don't really want to throw another $2,000 at it.