I have a firetec as the Heritage Daus ones were not avialable at the time, they are both very similar kits:
http://www.vwheritage.com/vw_spares_Fire-Extinguisher-DAUS-Low-Pressure-1Kg-Dry-Powder-Vertical-AC999E001_act_shop.product_pID_139050754_lang_EN_country_GB.htm" onclick="window.open(this.href);return false;
I am very unsure about the gas systems doing the rounds at the moment as a van engine bay is desinged to suck cool air in one side and move it out the other so in my mind the gas would clear pretty fast risking it re-igniting, powder may be messy but it works, hence why its used by all motorsports.