Thanks everyone
Asdaq, the bottom is just the sheet brass brazed to the tube and the top is the only opening. The caps I used for the first one were made out of steel that was chrome plated and they would slide off the tube a lot so thats why a made another.
cos, I made the horseshoe bracket out of 3/16 brass rod that I filed the sides flat so using square brass stock would make more sense (but round rod was all I had around). I used a broom stick to bend it around. The brass tube is 1/16 so I drilled the same size hole in the brass top cap then heated the 1/16 tube and used it to make the hole the right size in the plastic bottle cap. It will just melt it the correct size. I kept it on its side all day on my bench, then in my pocket for a while and so far no leaks. The horseshoe bracket works great with my GG, I screw the telescope sections down on the bracket so it clamps it nicely. I tried it on another tube style mod, it works but it wants to move a bit. Maybe I can find a better way to attach it if I am using another mod.