Welding Near Gas Tank?

I am going to weld floor pans in my 72 D100. This will be the first time I ever tried welding. I think I can cut out the old and fit the new pans. I think I will lap weld them in instead of butt welding. Anyway, there is a gas tank behind the front seat in the truck. What should I do, cover it with a welding blanket or drain it and remove it? Any advice will be appreciated. Thanks FABO.