Gas dry and Heet are the same. Isopropyl alcohol. They don't really "dry" the gas. They just bind the moisture and it is all burned together. But, if you have gross water contamination, it is not going to fix the problem.

I think you have identified the problem. Originally, it sounded like you had just 1 or 2 broken screws, but you have a lot missing and it is most likely not sealing.

If I were you, I would just drop the tank and fix it. Drain the gas, wash out the tank with a hose (if you have water, you have dirt, rocks, rodents ect in there). Then drill out the broken screws and chase the threads with a tap. Get a new gasket (I think there is a gasket) and put it all back together correctly.

Slathering on sealant from below with the tank in place is not going to last long. It is too dirty for the sealant to adhere very well or for very long.

Good Luck,
Michael

PS, the only other thing for you to maybe check is the idle air control valve located on the passenger side of the engine, under the intake. There is a large u-shaped hose that connects it to the intake. If it is loose, cracked or disconnected, your vehicle might start and run at higher RPMs, but it will not stay running. Or the valve may be sticking. Smack it a few times to see if anything changes.