Cheese Wagon also has me thinking about how to get the exhaust coming out the top, instead of out the back. I will be pulling my Charger on a trailer and I'm not crazy about the exhaust blowing all over the nice paint job. Coming out the top would eliminate that as well as get the smell up away from us. My wife has asthma and I have had CO poisoning which has made me lass tolerant of CO, so getting that up away from us sounds like a great idea. Rebuilding the back end should make that easier.
A wise decision, especially as your wife has asthma. I have real-world experience with this that I think would help you. Granted, I think there were slight oil and fuel injector leaks as well, but on my recent adventure transporting Mandinee1's Blue Bird (sister to your bus, I believe) from IA to the NorthEast, with my car in tow, my poor Toyota was getting a bath in carbon and oil -- literally.
The oil (and possibly fuel) wasn't that bad, but the Blue Bird's exhaust exited straight out the rear through a hole in the bumper, and every bit of smoke, oil or carbon that blew out that exhaust pipe was coating my hood, grille, front bumper, and headlights -- all plastic / polyeurethane except for the hood.
Fortunately, there was no permanent damage, as a quick trip to a high-pressure automated car wash took care of it. Though the car still slightly smelled of carbon for a few days after -- not good for my asthma, but it did go away after a few days. Something I think should be taken into consideration if pulling a toad.
However, given the high temperature of exhaust gases in general, especially diesel / LPG and CNG exhaust, combined with the excessive use of plastics in vehicle body parts since the late 1980s, I think it's a wise notion to keep your exhaust from blowing directly on your toad. Either that or fabricate a shield for use with a dolly or trailer to block the exhaust gases from blowing directly on the toad. But that doesn't address the issue of your wife's asthma.
My original idea would have been to cut and rotate the curved left or right rear body corner 180 degrees, welding it back in place. This would create a concave channel for an exhaust stack to fit neatly into. I would suggest making this area about 6" x 6" or even 8" x 8", for proper clearance of the pipe. The idea here, quite simply, is to basically shrink / invert the body on one corner to allow the exhaust to run up the corner without being inside the body.
However, upon looking at pictures of the shape of this area in such buses, some appear to have an inward rear slant from the window line up. So perhaps a better idea would be to cut a 6 – 8 inch section out of the side of the body just ahead of this slant, then cut a length of pipe in half length-wise (creating a C-shaped / U-shaped channel), welding this channel in to replace the removed section.
This would do the same thing and be able to run all the way to the top without a lot of fuss and muss, as well as keeping the exhaust from running inside the body, and helping to keep the pipe from hanging up on its surroundings. I'll try to put this into some kind of illustration later on in my original thread.
I would also suggest enclosing the exhaust pipe in heat wrap (Summit Performance sells this for the purpose of wrapping headers on drag race cars) to minimize heat transfer through the body and insulation. And should you take this suggestion, I would advise heavy investigation and eyeballing things in choosing which corner (left or right) you use, as you don't want to cut into radiator mounts, power steering lines, etc.
There is also proper routing of turbo plumbing to consider as well, which may well dictate which corner would be best for this method. I think it would work well, but I would also suggest replacing the rear emergency exit weatherstripping (possibly window weatherstripping as well) to be absolutely sure there is no opportunity for fumes to come in through those areas.
I think it goes without saying, but an exhaust flap like the one pictured would be a very good idea for this, to prevent rain from entering the pipe and backing up into the turbo and engine... You don't see them factory-installed on a lot of equipment much anymore, but that doesn't mean it's not a good idea.
Thanks for the pic it saved me a ton of time.
