bunk warmer only works when it's NOT cold outside

The Espar and Wasbo heaters look very much a like, and from the parts I saw, they were both made in Germany. As noted, the unit works well when temperatures outside aren't real cold, so the fan is OK, and so maybe the idea of gelling diesel has merit. I've heard now from several places the kerosene cleaning method described, but wasn't sure if I might somehow damage the unit. Now I know I won't. I like Pablo-UA's idea of mixing jet fuel and diesel, but can't I use a similar mixture of kerosene and diesel. I don't know where to buy jet fuel, but kerosene can be found at Walmart, I believe. 3 gallons is enough for a cold Ukrainian winter night? I'll want a week's storage, and maybe 3 gals is enough.