I find it interesting that the designers never thought about a chassis vent system. GMC M211's and M135's came factory with them. They used huge 1" steel tubing along the frame rails and it T's off in several places to smaller steel lines which go to things like the fuel tank, transfer case, master cylinder, air pack and air compressor. Rubber flex lines connect the transmission, engine and all 3 axles to the venting system. In fact, the flexible rubber lines for the axle vents are the same as the actual brake lines for ease of parts logistics in field.
The entire chassis vent system collects under the hood at the top of the firewall where it has a threaded fitting that is filled with horse hair to act as a filter. It sits directly in front of the 302's oil bath air cleaner intake hole so anything coming out of the chassis vent system is automatically pulled into the air intake. Eat that greenie weenies....