Here is what I came up with to remove the dent in my fuel tank. It's just a big u-bolt I had lying around with a nut on one end wrapped in tape. This u-bolt was used to attach leaf springs to a Jeep axle, but you can get curved and square ones in a variety of widths and lengths.  I got 2 people to hold the tank; then I inserted the u-bolt so that the tape-wrapped nut was under the dent.  Then I pulled hard on the bolt, and the dent popped out!  The repair isn't perfect, but it's good enough for me.  Just another idea.
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