The denialist interpretation is that the three camps Belzec, Sobibor and Treblinka were transit camps with disinfestation facilties using steam, which were misinterpreted as homicidal devices.Your apparent desired interpretation, that steam related to disinfection facilities in a transit camp, is a denialist interpretation as far as we are concerned.
My interpretation is not that at all.
It is that descriptions of genuine transit camps with steam disinfestation facilities became confused with descriptions of the extermination camps at a very early stage, when the both the Polish and Jewish Underground began to try to collect information about the mysterious new camps to which Jews were being shipped and disappearing.
Such a confusion is easy to understand, since the newly built camps outwardly resembled standard transit camps, which were divided into a clean side and a dirty side, with the disinfestation facility situated on the divide. The new camps followed the same pattern; for example, Yankel Wiernik describes Treblinka as being divided into two halves separated by a fence, with the first gas chamber situated on that fence, with the entry on one side and the exit for the bodies on the other.
The homicidal gas chambers also resembled disinfestation chambers, with an entry on one side (for infested clothing or for living victims) and the exit on the other side (for disinfested clothing or bodies of victims).
The resemblance of the new camps into which Jews were disappearing, and presumably being killed, was not coincidental, but most probably due to the fact that the German constructors of the extermination camps modelled them directly on standard transit camps (because they had nothing else to model this entirely new installation on).
The most likely reaction of observers was that if these new camps looked like transit camps, with which the observers were already familiar, but Jews were going into them but not coming out, then the Germans must have found a way of using the steam disinfestation facilities to kill people.
It was obviously a mystery to Polish and Jewish observers how steam could be used homicidally; one theory that was developed to explain it is that the steam entering the chamber forced out the air, so that the victims suffocated.
In summary, the denialist view is : the camps at Belzec, Sobibor and Treblinka resembled standard transit camps, therefore they were ordinary transit camps, using steam disinfestation facilities, and not killing centres of any sort.
My view is that the camps at Belzec, Sobibor and Treblinka resembled standard transit camps simply because in their design and layout they were modelled on such camps, with the standard facilities adapted for a homicidal purpose. Observers also noticed the resemblance, and jumped to the conclusion that the adaptation of the camp design to a homicidal purpose also included the adaptation of the disinfestation agent, steam, to that homicidal purpose.
The mysterious delayed action gas, which according to an early report of the Polish Underground was used at Treblinka II, is most likely to be explained by confusion between the new camp near Treblinka I, at which transports of Jews from Warsaw were observed to be terminating and the Jews disappearing, and a normal transit camp somewhere else. Possibly an agent of the Polish Underground, sent to look for the new camp near Treblinka I, found his way to at transit camp somewhere where he observed people getting off a train, going into a building like a bathhouse and coming out the other side, and then disappearing into another part of the camp. In the mistaken belief that he had seen the new Treblinka camp, he reported back to the Polish Underground what he had observed. Since the Polish Underground had correctly concluded, on the basis of what had already been observed at Belzec and Sobibor, that the transports of Jews arriving at the new Treblinka camp were being killed there, it interpreted this new item of information as indicating the use of some sort of delayed-action gas, which did not take effect until after the still-living and conscious victims had walked out of the gas chamber on their own feet.