Short story:
I poured in Sahara sealer and miscalculated the amount - too much. I tried to withdraw some of it with a plastic syringe, and while inserting a flexible plastic hose into the valve, I punctured the wall of the inner tube. It went straight thru like paper. I tried to inflate it and see if Sahara would seal it. It didn't. I pulled the inner tube out a bit and discovered a tiny puncture (2mm) like 1 inch away from the valve. I applied a Slime repair patch, pushed the inner tube inside, and had to use pliers to pull on the valve. Valve got smashed up a bit. I inflated the tire - it held fine for about 5 min, and then it deflated. I pulled the inner tube out again and discovered a much bigger tear all around the valve.
The tube is definitely super thin. Sahara sealer sucks.
Definitely need tube with a ticker wall. I searched the Amazon and found this one (but i'm not sure about the quality). Just ordered 16x3 here https://www.ewheels.com/product-category/innertubes/