this is a fantastic idea for anyone with alot of space!!
my dad has Diesel and Gasoline tanks in his yard, mainly because he has a truck service as well as car rentals but its still good to have around
so far what he has done was made a huge containment unit out of stainless steel, in the shape of a cuboid , then a smaller one inside to which the liquid is held
the space inbetween has alot of insultation like rubber and stuff that he usually doesnt use, he throws it in there
he has it 3 meters off the ground and the hose to fill is directly underneath the enclosure
i will get any info i can on the law and permits that may be required to build and store this, and any further build information for you!