My 85 pickup has rusted out. The gravel road has calcium salt added, and the paved roads use salt too, so when I get home in wet weather, there's salty mud coating the underside of my truck. I live offgrid without pressurized water, so washing the mud off isn't feasible (and it's really sticky mud), and it's sub-zero for 1/2 the year. Is it feasible to add an undertray? I think I could fab something from sheet metal, or maybe even a tough tarp. What I don't know is whether that blocks necessary airflow, or causes some other problem. An opening at the rear should allow airflow. I suppose I could add thermal sensors to the tranny and differential to watch for overheating. Adding an undertray seems like a good solution for road salt, and protects parts from bouncing rocks too. I'm a bit surprised that there's not a bunch of "How to"'s on the web, or offers of aftermarket products.