The thought of deploying a 40cm Krupp Howitzer in a skirmish game does have its appeal it has to be said
However, there are lot cheaper options for knocking out armoured vehicles, namely weapons that ignore armour, i.e. Arc and Flaming weapons. After all the armoured vehicles of the late 19th century were fairly ramshackle and rudimentary affairs and not yet immune to such weaponry.
As for the Society of Thule and the use of poison gas there shall soon be a company to be released on the blog that might be right up your strasse. I can say no more