Adding a sump in tank

I have questions about the safest method of welding a sump into my existing fuel tank. I really dont want to lose my spare tire well so I dont want to go with a fuel cell. However I dont want to risk a tank exploding and injuring anyone so a fuel cell may be the answer.

What methods have others used that eliminate possible tank explosion?
I have heard of using argon or nitrogen, however I dont understand how this works since there will be holes drilled into the tank allowing gases to escape.

Now if I have to go with a fuel cell are there any options for keeping the spare tire well? I want to use a 16 gal cell if this is my option for safety.

Thanks for any suggestions and information on this subject, By the way my car is a 66 Dart.

Rodney