John,
Neither example you just posted said the tanks exploded on impact. They just leaked out fuel when the filler is pointed down in a roll over, just like any style of fuel tank would.
An in-cab tank only has it's profile pointing toward a potential impact with another car. It's also protected by the door pillar and door. It's also mounted above the frame inside the cab where it's protected from the weather and road debris.
A rear frame mounted tank could possible be opened up just by backing over something (seen it first hand), not possible with the cab style. Anyway, enough of the [censored] match. I did move my in cab tank to the rear of the frame on my 63 but not for safety reasons. I did it to add stereo equipment. Also, this truck sits about 3 feet off the ground and will not be driven daily. The weather won't have an effect on it at all. It's also encased in a class 3 receiver hitch to help in a rearend collision, or if a trailer would happen to come loose and start stabbing at the tank. It may even get a skid plate before it's done too.
There's my "common horse sense", whatever THAT is,
Scott
