i ordered 5 ltres of ebay yesturday.... in my experience so far over the past 2 winters i have managed ok without isopropyl, but on really cold days its been difficult untill after 9.30, but once the sun comes up its been ok. i make sure i put a heater in the van overnight......
when i have to use isopropyl i will use my back pack, as then i will only need to add a drop at a time, rather than put a litre in my van mount..