The car did come with a seal for the trunk ( boot ). However it had been mounted to the rim around the boot on the car rather than on the boot lid. This meant that it would allow water in. Which I discovered after washing it for the first time.
So new seal has now been stuck to the lid. With some adjustments to the boot lid it closes really well now. With any luck everything will stay dry inside the car next time I wash it.
As an added benefit the better seal now means that the exhaust gases don’t get sucked into the car anymore. This has made driving a lot more pleasant.