Some gas tank questions

[olddog]

I have had gas fumes in my trunk and have had a small leak drip under the car if you fill the tank, since I bought the car. I finally got around to pulling the tank. I filled it with water to find the leak. Then removed fuel pump (EFI) and fuel gauge sending unit (two separate holes). Tank is made of a heavy gauge sheet metal ~1/16" thick and bare metal on the inside.

Two leaks: 1) fuel gauge sending unit was poorly installed. 2) the vent tube on the fuel pump is poorly designed.


Questions:
I see what looks like light surface rust inside tank. Perhaps my putting water in it caused it, but it was only in it a few minutes. Normal? Should I consider an epoxy coating for fuel tanks?

Fuel sending unit had sheet metal screws into tank. Fuel pump has a decent design where there is a thick ring inside the tank that bolts thread into. I would like to make something similar for the sending unit. Is the sheet metal screws plenty good enough or should I make a ring to bolt to?

Fuel pump has a vent on it and the fuel tank has a vent near the fill neck (opposite sides of tank). I don't see a need for two vents. I would like to plug the vent on the fuel pump. Any reason not to? BTW the EFI uses a return line.

I may have some more questions later.