I have been running my 300tdi Discovery over the last 2 years and covered 25k. The only way to go is a twin tank setup with heat exchanger so that you only run on 100% veg oil when the disco is warm. The key is to remember to switch back to diesel at the end of your journey. I have a second disco tank in the boot wired into the fuel guage so when you switch over your fuel guage flicks over also. This winter has not been that cold, but even last year the oil remained fluid and worked well.
The key to good oil is time. Leave to settle for three week in warm conditions (100w bulb works well!) and make sure that there is no water in the mix.
Hope this helps - happy motoring!