In reply to the suggestion by Chris: "it would be awesome if you could take some pictures of what you had to do. I say that because we need a good write-up detailing how to do this, since there isn't one out there I can find, not even on YouTube!"
First, here is a picture of my gas tank, dropped from my 1998 Wrangler SE. If you enlarge this you can read that it is part no. 52018687AB, what Jeep lists as the 15-gallon tank.
The picture also shows the two tubes: the thicker fuel filler tube and the thinner vent tube. Next is a picture of the inside of this tank, showing where the two tubes come in.
As many have said, you only need to cut off the thinner vent tube protruding inside the tank, not the thicker fuel filler tube. You do this by feel, since you cannot see inside the tank. The easiest way to do this is with a "PVC Cutter." This also makes a very smooth cut.
For those who are inexperienced, or mechanically challenged, or both (like me), it may be necessary to figure out the PVC Cutter. They are available from Home Depot for under $10, and from Harbor Freight for $7.50. They are all made in China, so it doesn't matter which one you get. They come with the blade closed, with no button to open it, and no instructions. As I learned from YouTube, you have to pull apart the two handles to open the blade. Then reach inside the tank with it, place it up against the side of the tank and around the vent tube that you want to cut, and start squeezing the two handles together to ratchet it closed. The first couple ratchetings are not cutting anything, then it engages the tube and cuts it easily like butter. As can be seen in the above picture, it leaves about 1/4 inch of the vent tube still protruding inside the tank. This cuts off about four and a half inches of vent tube, which can be seen along with the PVC Cutter in the picture below.
