In all likelihood the leak was due to a poor weld on the seam rather than any road debris. We had a defective tank on our 2001 Winnebago Adventurer. It turned out to be a bad weld at the blow out plug seam. The seams are robotically welded, and apparently the welder stopped about a eighth of an inch from where it should have.
We chased the leak for over a year with no results. On occasion we could smell the gas but could never find the leak using soapy water, a sniffer, or any other method. It was only a pin hole size leak that was intermittent. Apparently from time to time crud would cover the hole and the internal pressure would hold it in place. After a days drive there would be enough jostling that the crud would be displaced. We would smell gas when we set up camp, then it would disappear when another piece of crud migrated to the hole and plugged it.
We finally found it one 4th of July weekend when camped in a state park. The smell just wouldn't go away and it made us a bit nervous with all the fireworks going off in the campground. On this occasion I took a bottle of soapy water and sprayed the entire tank liberally. It didn't take long for the leak to become obvious.
We called a local gas company to come out and drain the tank, but since there was no liquid fill port it would have needed to be transferred in a gaseous form to several empty tanks. The technician tried draining it that way but gave up after he'd filled half a dozen tanks and barely touched the volume in our tank. He had us drive several miles to a field. Once well into the field he attached over 100 feet of hose to the gas fill port and slowly drained the tank. I think it took over an hour to empty it without raising the concentration levels to the point an errant spark would ignite it.
The tank was replaced under the manufacturers warranty. Ours was a Manchester tank that was guaranteed for 10 years against defects. Your tank should have a data plate welded to the side near the fill port. That plate will give the date of manufacture, serial number and other information pertinent size and warranty information.