strong gas fumes inside car and poor gas mileage/evaporated

I got in car to go to work and smelled VERY strong gas fumes before even starting it. I got out to see if gas was leaking from tank under car. (No puddle evident) I drove 5 miles and had to return home because I became nauseated/headache and eyes burning. I immediately made appointment fearing car may blow up. When I moved my car from my parking space, there never was a gas smell left behind (like from a dripping gas line). I noticed even though I had just filled up, my gas gauge was reading way under a full tank.

I was VERY upset that the "nipple" at the top of gas tank connecting gas lines was the only thing "chewed" or "dry rotted" (like old tires), but the ENTIRE gas tank had to be replaced, even though gas tank AND fuel lines were fine. REALLY? ...on a 7 yr. old vehicle? I've had 20 yr. old cars, living out in the woods on a farm that NEVER had this issue.

Is this made with soybeans like wiring harnass complaints in engines where rodents are eating them as well? Unable to determine if rodents or "age" of nipple was the problem.