Permatex makes a plastic gas tank repair kit. Most of the big box retailers carry it. It's like $9.99 Especially if that hole is on the top it should do fine. Are you sure that your rollover valves aren't the leak?
"It's not about how hard you can hit, it's about how hard you can get hit and keep moving forward!"
I'm in the same boat....my 84 CJ7 Laredo has the factory 20 gal tank, mine has a crack on the top "curve", I was able to get it to seal with some epoxy but I don't ever fill it all the way just in case. I have seen 20 gal tank kits on Ebay that are geared more towards the guys who want to upgrade from the stock steel tank but they are pricey....$300+
I used the tank repair kit with the braided material.. cleaned the area real good, applied the stuff and the material.. when it set up, I used that liquid metal 2 part epoxy to coat the heck out of it.. then covered it all with the metal (chrome looking) tape.. sealed up great..
I want to die in my sleep like my grandfather, not screaming in terror like the passengers in his JEEP!...
Try the plastic welder from Harbor Freight. I used the one that is about $70
Just make sure the tank is empty and evacuated
( I put a hose on my lawn mower exhaust and ran into the tank for 20 minutes).
Follow directions that come with the welder.
So far this has lasted twice as long as the epoxy patch.