Alright, so I changed the coolant flow just as suggested. The oil gets warm now! Sweet smell of french fries, here I come !

However, I plan to change my whole oil tank setup (2 tanks for oil) and I'm open to suggestions. I will probably let someone custom weld them from aluminium. The first thing I need to figure out, is where to place the tanks. There are 2 obvious places:
a) inside the van, under the rear seat and in one of the closets
b) outside and under the van, on both two sides, where there is a pretty big space (some vans have a water tank or propane tank there)
That said, I also would need to mount a filter and a pump between the two tanks.
As I probably need to open the tanks for cleaning, I thought of a design, where all the connections to the tank (fuel in, fuel out, heating, fuel level senders etc) are mounted on the top cover, which I can remove somehow (either it is attached by screws or some other ingenius thing). This way I can just lift the cover away and clean or check the tank and the connections on the cover.
Benefits for A:
- Very easy to maintain, just open the closet/rear seat and remove the top cover
- Veggie oil stays a bit warmer during wintertime & driving
Cons:
- Takes away valuable closet space
- Could make the inside of the van messy when there is a leak or when I need to change the filter
Benefits for B:
- Will not take up valuable space, Good use of free space under the car
- No need to worry about interior getting messy or smelly
Cons:
- Removal of top cover would be a lot harder - actually it would mean to remove the whole tank and drop it to the ground and afterwards remove the top cover
- The connections are hidden behind the top conver so I cannot check their situation, I would need to remove the whole tank
- Oil can get really cold during wintertime
Any thoughts/ideas?