I have used the por 15 stuff before on my car gas tank. prep is the pain part, so it sticks.
but I also used it on a sending unit, where the weld was porous and leaked gas. It has held for 10 years or more with no issues.
I recall that the kit came with something to hold it in place for pin holes as well, but yours look much bigger.
If I were trying to do it, I agree with the others in using silver solder. you might check around for someone that can do it for you. might be cheaper than you think.

for instance when I was trying to weld the brackets on my aluminum radiator, I found a duct work shop that did it for like 40 bucks. vs the welding shops that wanted 100 just to spark and arc for it.