Warren, your mention of Ralph NADER brings back bad thoughts....
Your reference to a rear collision and the rupturing of the gas crossover is a possibility. I have made a sheet metal (20 gauge) panel to fit in under the soft top for one of my Alpines with the intention of eliminating a possible fire through the rear section of the trunk (gas tanks and fuel pipes/lines) into the passenger compartment.
It covers the entire openings from one side to the other between the inner fenders. Took quite a bit of time making a pattern for a decent fit that would help starve off a fire should I have an accident.
Bill Blue was rear ended when he was making a right turn into a driveway. It was a major hit to the right rear of his Alpine. It actually smashed the fuel tank but did not cause a fuel leakage by some miracle.
It sure enforces my desire to have that divider made for my Red GT.
If you go with an additional fuel tank of some sort, I wish you the best, but I have not yet figured a need for additional fuel tanks.
Procraft and Bradly did the Mustang style tanks in their Sunbeams and that tempted me a bit