I have some experience with this, Teflon tape is good for many things, but it will NOT work with gasoline. It will certainly leak if used on threads in fuel.
JB weld is also a great product, we use it at the shop for many purposes, but not for sealing threads, especially where gasoline is the substance in question. It would be good for bonding the two parts though.
The key is using something that won't be affected by gasoline and can seal without tiny air pockets because they will leak.
In the absence of welding equipment, or experience, -more on that below- you would need two different products to make it permanent, well nothing is really permanent, but you get the idea.
To seal the threads on the Fuel Fitting, use Permatex High Performance Thread Sealant. Gas will not eat away the sealant. Part number 25117(small) or 56521(large)
To make it a permanent fitting -in a 'weld-like' way- we use Permatex Epoxy Cups, they are not used to stop fuel leaks, that's why you need the thread sealant, but they bond dissimilar metals better than anything I've tried. Similar to JB weld, but thinner and easier to spread. Very strong. Part number 21425(small) or 21426(large) We get them in a 10 pack tin, I would use one or two large cups, mix it up and spread it on the pipe and housing, work quick, you don't have a lot of time before it sets.
Welding a fuel tank is not as difficult as you may think.
Here's how we do it; Drain fuel, wait a few minutes to vent fumes, fill with some water, swoosh it around, drain, fill again, swoosh, drain once more. Fill the tank with water one last time, just below the neck -or fitting- and leave it. Set up your equipment and weld while it's full with water. This is the only safe method when working with fuel tanks.
Drying is done with low heat, compressed air, or evaporation over time(or any combo thereof).
Good Luck with your project.