I've been asking about this recently and doing a bunch of research as well.  It seems the plastic is the best fix, if you are worried you can also do a rubber bladder inside the gas tank (I guess it requires being replaced every 5-6 years though) and that will keep the tank from leaking if it ruptures.

Those are good questions, and unfortunetly I have no good answer.  Anybody else?

I have been looking at various fuel cells.  It looks like I could mount one in the trunk above the rear axle and add a filler kit to be in the same fill location as the old tank.   Then remove the old tank.   
If I did that and removed the spare tire it ought to handle a lot better. 
What ya think? 
   

Ages ago I had a 1972 Mercury Capri which had similar drivetrains as the Pinto.   It had the gas tank in trunk behind the rear seat.   

Hi and i can understand your worry. But I can tell you that the recall setup that might be on the car already is more than enough.
 I have good friend that rebuilt a 72 hatch back in 82. His wife and 1 year old was i in the car when it was rear ended at 75mph at a red light by a 78 3/4 ton chevy truck.
 No fire or gas spillage and his wife just had bumps, bruises and whiplash. The baby was fine. Car was absolutly destroyed though.
 The only reason the tank ever had a problem was because of the 6 3/4 rear differental cover . It has a sharp edge all the way around it. The tank used to get split because of the impact up against the edge. ALSO the original filler tube was too short. It used to get pulled out of the tank and therby giving another spot to let the gas spill out.
 The sparks from grinding metal against the spilled gas was the only reason for the fires. The car never really "exploded"
 Anyways my  2c