I made a lot of mistakes, but
The main body, fuel tank, and electric pump can all be installed neatly under the floor.
It was a great satisfaction.
Even if the outside of the car is below freezing, the inside of the car is warm and comfortable.
If you install the FF heater, you can enjoy staying in the car even in winter in Hokkaido.
Equipment and items purchased and used.
2000W FF heater
https://amzn.to/3rO6OoN