Do you store your car in a garage? I would think that while having the tank vent outside the body would keep the trunk from smelling, it would just move the fumes to the volume of your garage. Sure, it would be diluted, but that would be a no go in my house.
The carbon canister in my US version 1970 2800cs, if it had one, is missing and the container above the gas tank is severely cracked. So I plan to install a all new gas fume recovery system with all new parts during the restoration to avoid any future issues with gas smell and thus the Mrs.
I did buy an import hydrocarbon sniffer to help with finding the source of a gas smell in another car, and while not cheap, it wasn't anywhere sensitive enough to find a small leak. It did sing when pointed at a large amount of fuel, but it was no help in pinpointing the source of the smell. I'd hope there are very good instruments out there that can do the trick, but probably priced beyond what most hobbyists would want to pay.