I'm in Prince Edward Island, so we have it even worse than you. Not only do we have road salt in the winter months, we are surrounded by salt water! We add time for these things regularly, depending on the car. If it's especially rusty looking my techs will usually give the SA a heads up that there may be extra time involved, and this is relayed to the client. They have gotten pretty good at spotting something and letting us know that it may cause some extra time the vehicle. That said, the rust doesn't often slow my guys down much, aside from wheel alignments. One trick we use for those tight spots such as your fan shroud.....keep a few various sizes of tin laying around the shop to use as a heat shield between the part you are heating and the part you do not want to burn/melt. Works great. Also, Wurth makes a spray gel designed to protect things from welding sparks, that can be sprayed on plastic or other pieces that helps them withstand heat better. I can send you a picture of the product tomorrow from the shop if you like.