If you have the bigger tank (7.5 gallons) then there is a pre made one available. It says it will also fit earlier cars with the smaller tank (I assume there will be a small gap on that side)
https://minikingdomonline.com.au/product/boot-liner/Also flat ones:
http://minisport.com.au/mini-boot-board ... 5gal-tankshttp://minisport.com.au/mini-boot-board ... tank-minisIf you want a lining kit for the boot lid:
http://minisport.com.au/boot-lid-liner- ... o-cooper-sYou can also buy some plywood or similar from a hardware shop and cut them to size