How to seal Air tank?

[bagged69chevy]

I made a custom Air tank and have a few pin holes in it. I plan on welding the pin holes up but am worried because i have quite a few seams/welds I'm worried will degrade over time due to moisture and fatigue. Is there a coating i can coat the inside of the tank with that will help protect the welds form the inside; and possibly seal up microscopic pin holes?

Ive heard some guys talking about gas tank sealants but didn't know if that would work for air tanks under 150-200psi pressures.

also.. the tank is the back half or my frame.. so thoughts on that as well. Has that be done successfully? (keep in mind this is not a daily driver, but will be driven from time to time)

And not to be a jerk, I know guys like to give their opinion even though they have no first hand knowledge on the subject. Im looking for informed opinions on the topic; this is going to be a sema truck and want to make sure its done right the first time. We have spent countless hours making the frame work as an air tank and really want to make it work if possible. Holding safety and functionality above everything.

Thanks guys