A good modern sealant for fuel tank halves is Pematex Anaerobic Sealant. A thin coat on each clean half, and also on the clean screws will work provided there are no deep gouges in the mating surfaces.

Any leftover sealant from the factory must be removed. Have everything super clean, and ready to go. Don’t waste a lot of time installing the fasteners. You don’t have to rush, just stay busy, and finish the job before the anaerobic cures.