There are only TWO reasons that I can think of to have stacks:
1: Your 'rig' is an 18 wheeler (duh)
2: To bring the exhaust up to clear very deep water crossings (and this is stretching it)
Although, reason 2 is rarely applicable due to the fact that most do not waterproof the engine.
the ONLY thing i could see this doing is getting your exhaust up and over your enormous fifth wheel.... but this guy prob dont even got a fifthwheel
