If it was mine I would do some inside tank cleaning chemical treatment. Then tape up all the holes and apply some air pressure with a soapy exterior wash looking for bubbles. I'd also make sure the drains work and don't leak after teflon tape treatment. Next I'd look for an ethanol proof liner treatment. Some liner treatment are way better than others do your research!
I had a seam weep back about 85 in my 72. I did the JC Whitney ethanol liner. The inside of the tank looked like new so I didn't do the chemical cleaning. I used some gas tank epoxy to build up the area on the outside of the tank where the pads has caused some pitting from dampness - It was a rag top from 72-80.
I sort of miss my aux tank. It was really handy for the back country where there is no gas station. I would just pull the hose off the carb, plug on my fuel hose extension, flip on the key and fill up my 4 wheeler with the electric fuel pump.