"There are no PBGC regulations interpreting this exemption and only a few PBGC advisory opinions referencing certain aspects of the exemption. Of the more than 2,500 federal court cases dealing with union pension plan withdrawal liability, less than 30 cases refer to the trucking industry exemption and most of those 30 decisions do not deal with the qualifying requirements for the exemption but rather pertain to routine withdrawal liability issues such as arbitration deadlines, controlled group liability, 'evade and avoid' issues and bankruptcy."