I just put downspouts on my diesel pickups glass packs that dump just past the rear axle tubes,and the smell does get in the cab a bit,especially with the rear slider open while moving...but not enough to bother me all that much--when I first got a diesel VW jetta,I hated the smell of diesel fumes,but after awhile I guess you get used to them...gets in your blood!.........................................................................................................but if I had no worries about passing inspection,I'd just assume put stacks on it ,then I wouldn't get any odor at all,and I like the looks of stacks as long as they aren't outrageously large like stovepipes...............................................................................................I may add a few feet of straight pipe to the mufflers and run the downspouts out the back of the truck--I noticed soot is accumulating on my rear axle tubes and brake lines!..--if I drove it more and further I'd probably have done it already..sometimes pipes sticking straight out the back dont get the fumes away from the truck as much as you'd think though too--.I've had tailpipes that exited in front of the rear wheels on other trucks,and they didn't get rid of the fumes as well as ones dumping behind the rear wheels ..