Why would they need 800 stokers for one body at a time?The crematoria you are referring to were standard in all German camps they were only capable of cremating on body at a time, as for gas tight doors these were aslo standard in all german air raid shelters and delousing facilities.What about surviving German written records. There are thousands that can be looked up quite easily and they are copies of the original documents so can't be explained away easily. Many refer to crematoria ovens and improving efficiency and throughput. Dozens refer to needing more ovens urgently. One I saw said that capacity was 1850 corpses per day and this was not sufficient and more ovens are needed urgently. Many refer to research on ovens and how to improve them. Many are giving feedback on new ovens and increased efficiency. One refers to ordering a new 'ball mill' for "special substances" at Chelmno. Dozens list 'special' construction projects. Dozens refer to orders for new 'gas doors' and various other equipment. One interesting one refers to the labour force at Auschwitz; 870 stokers and 30 wood loaders for the crematoria. And that's despite the fact that you claim no smoke was ever seen coming from the ovens! What were those stokers up to do you think? There are thousands more records, some recovered from filing cabinets and some intercepted. Apart from memos, letters and reports there are a number of officer diaries. These clearly refer to extermination - the Auschwitz doctor himself refers to the camp as "the Auschwitz camp of extermination". Plus there are literally thousands of photographs of piles of corpses and mass burial pits.
What's the conspiracy line on those documents?
This Auschwitz report in October 1941 says that 60 men can be cremated in one hour.
The Topf engineer that developed and built the ovens said in a letter that "the number of muffles [37 with a capacity of 1850 corpses per day] is not yet sufficient; we should deliver more ovens as quick as possible".
Again these aren't accounts given after the event they are contemporary letters and correspondence from people involved at the time. Why would they have even mentioned such things if it wasn't what they saw, witnessed or knew of.