With regards the flimsy doors: the argument goes that they would have used heavy metal doors at the time, like they had on the fumigation chambers for clothes, but they were removed.

The problem is the walls in the alleged gassing chambers / shower rooms that would have supported those doors were very thin partition walls, added in after the building was complete, and could not support much weight.

You have to specially construct walls to be strong enough to hold those style of heavy metal doors. The fumigation building was especially constructed for that purpose (gassing the clothes to kill lice) and so could support the doors.

This stuff about the thin walls was only noticed recently by an Italian engineer studying the plans, obviously many years after the Zundel trial.