80s BRAT and wagon fuel tank repair. Internal pick up lines

[SiriusBlack]

I have an 86 BRAT that has a leaky fuel tank. Now as many of you probably know you can't get new tanks for these. I've cleaned it up and repaired it about 90% of the way, I used some sheet metal and solder. However my solder joints leak in a couple places and refuse to seal. Does anyone know if something like red line tank sealant is safe to use? The insides of these tanks have a web of fuel pick up lines, which is why I haven't used a sealant even after all this time. For fear of it sealing those lines and ruining my tank. Any help is appreciated, thanks in advance.