Giving this thread a resurrection as I found my heater starting to play up, run for an hour or so then shut down, copious amounts of smoke from exhaust, so it shut down with a high exhaust temp alarm, thinking about it I shortened the exhaust to the original length of about a metre and once it had cooled down, cleared codes and refired it up, running well now..........
I had read that without a muffler it could run an exhaust to 5m, mine was about 3m now its 1m and the end is about the middle of the van, plan is to see if an exhaust shop can make me a pipe of say 40mm with a 25mm reducer on the end to hook up to the heater exhaust, this should allow enough flow to not upset the sensors and enable the exhaust to get clear of the underside of the van...................had no option but fit heater awning side near the wheels so a long run to vent exhaust away from everything.
No fumes or anything getting into van but would prefer not to dump under the rig.......