Welding metal together is easy.
KNOWING & UNDERSTANDING what is going on in the puddle & area around it is something else entirely.
In my work I see lots of 'professional' welders. Some are good & know what they're doing. Some, not so much.
Some think that they are experts since they can strike an arc.
If I HAD to have a fuel tank welded on, I'd hire it out (based on recommendations & past performance) & have them call me when they're finished. That way I avoid the risk to what is really important - me, myself & I.
Some things ain't worth the potential savings. . . .
Good luck in whatever path you take.