There was a recall of 1996 Geo Trackers because the gas tank construction was of poor quality and vulnerable to rupture if someone hit the car from behind. There were cases of vehicles being hit and then exploding (I think something like the old Ford Pintos). So a recall went into effect but only for one model (the 2-door or 4-door? Don't know) even though both models had the very same tank. In years after, the defect may have been corrected but I tend to be suspicious about things like that. I would want no part of any gas tank ever put on a Tracker. Where there's smoke, there's fire, you know? So, if I were you, and since it looks like you are not afraid of really rebuilding something, I would just take out the tank and replace with something really strong from another vehicle altogether and then even rig some type of cage around it since it is so close to the rear. I saw the story on this on television recently but it is probably also on line somewhere.