Yes.
Middle of winter, windows up no bulkhead just been working with a faulty boiler and you drive off. Can't be good can it?
I would have thought hot gasses would rise rather than sink to the floor and out of the van that way. The fogwash I have isn't particularly well sealed at the vent so I would imagine much of the gas would come back through the gap at the top. I don't think it's simply hot air that comes out of the exhaust.
Obviously you have made your mind up so carry on. 
"Burned LPG creates deadly carbon monoxide emissions. Never use LPG appliances indoors without approved ventilation. Be cautious of LPG powered lifts while working in areas like warehouses, freezers, container vans or any other environment with limited ventilation."
Okay, maybe I wasn't clear enough Mark.
According to some people, using LPG heaters is the most dangerous thing you can do, and if you don't die from a ball of fire consuming the entire van, you will die a horrible death from toxic fumes or fall asleep in the van never to wake up again. I would not be here typing to you if any of the above were true in my case. Don't get me wrong, I'm not saying people should be using a hotwash without proper ventilation, but things shouldn't be exaggerated.
The CO2 sensor trips almost all the time, and that is with a enlarged flue going straight up through a mushroom vent. Even though the van is properly ventilated and exhaust gases go out of the van almost immediately. Even with the back doors open, this happened frequently to me. Many people find this to be a problem, including me, and have therefore bypassed the CO2 sensor.
This in no way makes the boiler a faulty boiler.If I would be using the hotwash as it was designed to be used, as a shower, in an enclosed space with little ventilation, standing in the same room for 20 min having a nice wash, I would leave the sensor in place. I'm not crazy.
I'm not actually in the van having a kip when the heater is on full wack either, I am obviously out working. The van is practically swiss cheese when it comes to ventilation to begin with. According to some people, just opening the back door and sticking my head in would calmly put me to sleep or die on the spot (lol) Heaven forbid actually stepping in the cab area and driving off! I've been working well over a year with the hotwash and there is no danger in that way, not in my van at least. I did not even have a bulkhead in my old van. I invested a lot of money in a Grippamax system just for personal safety, I'm not about to put my life in danger in any other way.
I also did not say that I would be using a 180 degree bend without testing it properly and without worrying about my personal safety. I said (among other things) :
It would all boil down to (excuse the pun) whether the exhaust fumes would go through the duct well enough. I will be getting a new flue somewhere this week anyway, would be easy enough to test this.
This is easy to test, as results of the exhaust fumes not clearing the 180 degree bend are easy enough to diagnose. As I said, I'm not overly concerned about ventilation due to the van being ventilated properly. I appreciate the risk of an excess of fumes building up, and if that is the case I'm not using the 180 degree bend that way. I am at the other hand not worried about the CO2 sensor tripping, as in most situations, that happens anyway.
Again, I'm not condoning or promoting modifying the heater or using it without proper ventilation.
As obviously other people are using a 180 degree bend without any problems, I was at least interested in how they get on.
But thanks for your concern.