[chittychittybangbang]

I'm 99% sure it won't get hot enough to warm up biodiesel or SVO. The reason people use the coolant lines for SVO is that there's a lot of coolant and it reaches a temp of about 190 F. There is not a large enough mass of fuel coming in the return line and it's also being cooled by the fuel tank, so I doubt it can noticeably heat up SVO. Maybe enough to warm up biodiesel but not enough so you can avoid additives during the winter and still use it.

 

[chittychittybangbang]

My car takes 12 miles just to warm up. Some suggestions: get a coolant block heater, google frostheater. This would be in addition to the inline electric heaters. You say that you don't drive the golf below 30*F, if you have another car I would just drive that instead of risking gelled fuel in the golf or other complications from cold fuel.

 

[chittychittybangbang]

I've never seen a cooler under the right seat :dunno

That's because it's not under the passenger seat, it's underneath the car around the pass seat location! If it were under the seat it would get pretty warm eh! It's also only on ALH engine automatic transmissions, pumpe duses also used a fuel cooler.